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Introduction

Skin bleaching, also referred to as skin lightening or depigmentation, involves the intentional use of cosmetic products to reduce melanin concentration and achieve a lighter skin tone. The practice is widely prevalent in Africa, Asia, and the Caribbean and is influenced by historical, sociocultural, and economic factors that associate lighter skin with beauty, privilege, and social mobility.

Globally, skin bleaching has emerged as a significant public health concern due to the widespread availability of products containing toxic chemical substances. Numerous investigations have shown that some skin-lightening products contain hazardous ingredients such as inorganic mercury, hydroquinone, and potent corticosteroids. Chronic exposure to these substances has been associated with dermatological damage, nephrotoxicity, neurotoxicity, endocrine disruption, and adverse reproductive outcomes.

In Zanzibar, cosmetic products are readily available in open markets, beauty salons, informal vendors, and small retail outlets, often without adequate regulatory oversight or post-market surveillance. Despite international conventions such as the Minamata Convention on Mercury, enforcement remains inconsistent in many low- and middle-income settings, allowing unsafe products to remain in circulation.

A major limitation in existing literature is the absence of integrated epidemiological and laboratory-based assessments specific to Zanzibar. Most studies focus either on self-reported cosmetic use or laboratory product testing alone. This study addresses that gap by combining population-based survey data with chemical analysis of cosmetic products to evaluate toxic exposure and associated health outcomes within a public health framework.

Literature Review

Skin bleaching is widely documented across Sub-Saharan Africa, South Asia, Southeast Asia, and the Caribbean. The practice is closely associated with colorism, colonial history, media influence, and socioeconomic perceptions that equate lighter skin tone with attractiveness, higher status, and improved life opportunities.

Several epidemiological studies conducted in Ghana, Nigeria, Tanzania, South Africa, and Zimbabwe report moderate to high prevalence rates of cosmetic skin-lightening practices among women of reproductive age, particularly in urban settings. Reported motivations include perceived beauty enhancement, peer influence, marital prospects, social acceptance, and occupational advantage.

Toxicological investigations consistently demonstrate that many skin-lightening products contain hazardous compounds. Inorganic mercury salts are frequently added for their melanin-inhibiting properties. Chronic mercury exposure is associated with nephrotoxicity, neurotoxicity, tremors, cognitive impairment, immune dysfunction, and reproductive complications. Mercury can cross the placental barrier and may affect fetal neurodevelopment.

Hydroquinone, another commonly detected compound, inhibits tyrosinase activity and reduces melanin production. Prolonged misuse is associated with exogenous ochronosis, skin irritation, dyschromia, and increased sensitivity to ultraviolet radiation. Many countries restrict or prohibit hydroquinone in cosmetic formulations, yet it remains widely available in informal markets.

Topical corticosteroids are often added to accelerate visible skin-lightening effects. Long-term use may result in skin atrophy, striae, acneiform eruptions, delayed wound healing, immunosuppression, and systemic endocrine disruption due to hypothalamic–pituitary–adrenal axis suppression.

Advanced analytical techniques such as Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) are widely used to detect heavy metals in cosmetic products, while High-Performance Liquid Chromatography (HPLC) is commonly used for restricted organic compounds. Despite international regulatory frameworks, weak enforcement, porous borders, informal supply chains, and limited consumer awareness contribute to the continued circulation of unsafe cosmetic products.

However, few studies in Zanzibar have combined epidemiological data with laboratory confirmation of toxic exposure. An integrated approach is essential for evidence-based public health policy and regulatory action.

Methodology

Study Design

A cross-sectional epidemiological study was conducted to assess the prevalence, patterns, and determinants of skin-bleaching practices and associated toxic cosmetic exposure among women in Zanzibar. The study integrated questionnaire-based epidemiological data with laboratory analysis of cosmetic products to characterize exposure to hazardous ingredients.

Study Area

The study was conducted on Unguja Island, Zanzibar, covering both urban and peri-urban settings where cosmetic product availability and usage are reported to be high. Sampling locations included residential communities, public markets, beauty salons, and retail cosmetic outlets. The area was selected due to the widespread presence of informal cosmetic markets and limited existing exposure data.

Study Population

The study population consisted of women aged 18–49 years residing in Unguja Island for at least six months prior to data collection. This age group was selected because of higher reported use of skin-bleaching products and potential reproductive health implications.

Inclusion Criteria

Participants were eligible if they:

Were aged 18 years or older

Were current or past users of skin-bleaching products

Had resided in Zanzibar for at least six months

Provided informed consent

Exclusion Criteria

Participants were excluded if they:

Declined to provide informed consent

Were temporary visitors to Zanzibar

Used only medically prescribed dermatological products

Presented expired or damaged cosmetic samples for testing

Sample Size Determination

Sample size was determined using the single population proportion formula:

n = Z² p(1 − p) / d²

Where:

Z = 1.96 at 95% confidence level

p = estimated prevalence of skin-bleaching practice

d = margin of error (5%)

Where applicable, finite population correction was applied. The final achieved sample size was 55 participants.

Sampling Technique

A multistage sampling approach was used. Districts within Unguja Island were stratified into urban and peri-urban areas. Beauty salons, community locations, and relaxation areas were identified within each stratum. Eligible and willing participants were selected using simple random or convenience sampling depending on site conditions.

Cosmetic products reported by participants were purposively sampled from households, salons, and local markets. Priority was given to commonly used products, products claiming rapid skin lightening, and products lacking regulatory labeling.

Data Collection Tools and Procedures

Data were collected using a structured, interviewer-administered questionnaire. The instrument was pretested and administered in Kiswahili by trained research assistants.

The questionnaire captured:

Sociodemographic characteristics

Skin-bleaching history and patterns of use

Duration and frequency of application

Body areas of application

Types and combinations of products used

Sources of cosmetic products

Motivations for use

Self-reported dermatological symptoms

Self-reported systemic health symptoms

Reproductive health indicators

Daily field checks were conducted to ensure completeness and consistency of collected data.

Cosmetic Product Sampling

Participants were asked to present products currently in use. Additional commonly used products were purchased from beauty salons, local markets, and informal street vendors.

Each product type was purchased in triplicate where possible to support analytical reproducibility. Samples were labeled with coded identifiers, catalogued, and stored under controlled conditions prior to laboratory analysis. Manufacturer identities were anonymized for reporting.

Laboratory Analysis

Heavy Metal Analysis by ICP-OES

Cosmetic samples were prepared using standardized acid digestion protocols. Heavy metal concentrations were quantified using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).

Analytes included:

Mercury (Hg)

Lead (Pb)

Cadmium (Cd)

Arsenic (As) where detectable

Calibration standards, procedural blanks, and quality control samples were analyzed to ensure measurement accuracy and precision. Results were compared with internationally recognized cosmetic safety limits (WHO and FDA reference thresholds).

Qualitative Label Review

Product labels were reviewed to identify declared active and inactive ingredients. Substances of toxicological concern — including hydroquinone, corticosteroids, formaldehyde, diethanolamine, and related compounds — were recorded based on label claims only. No confirmatory organic compound testing was performed for these substances.

Quality Assurance and Quality Control

Standard operating procedures were followed throughout data collection and laboratory analysis. Instruments were calibrated regularly. Duplicate analyses were conducted on selected samples. Questionnaire data were cross-checked daily for completeness and internal consistency.

Data Analysis

Data were entered and analyzed using statistical software. Descriptive statistics summarized prevalence, usage patterns, and exposure characteristics. Inferential analyses evaluated associations between cosmetic use and sociodemographic and health variables.

Laboratory findings were compared with international safety thresholds and integrated with questionnaire data for exposure assessment and public health interpretation.

Ethical Considerations

Ethical approval was obtained from the Zanzibar Health Research Ethics Committee. Written informed consent was obtained from all participants prior to enrollment. Confidentiality and anonymity were maintained throughout the study. Participants were informed of potential risks and advised on safer cosmetic practices.

Results

Sociodemographic Characteristics of Respondents

A total of 55 women participated in the study, with a mean age of 30 years. Most participants (60%) were aged 18–25 years, indicating that younger women formed the majority of cosmetic users in the study population.

Educational attainment was generally low. Most respondents had certificate-level education (65%), while smaller proportions had completed Form Two or below (15.8%), diploma level and above (12%), and Form Four (7.2%). This distribution suggests limited formal health-risk awareness capacity in the study population.

Occupationally, many participants were engaged in informal and high public-contact sectors. The largest group worked in hospitality and personal services, including drinking-den attendants and salon workers. Monthly income levels were generally low, with 45% earning TZS 100,000 or less per month, indicating socioeconomic vulnerability.

For epidemiological clarity, occupations were grouped into broader categories: hospitality and personal services, informal or unstable employment, formal employment, and domestic or indoor work. This grouping reduced misclassification and improved interpretability for exposure and socioeconomic risk analysis.

Note. Percentages are based on the total sample (N = 55) and may not sum to 100% due to rounding since

multiple responses were permitted; percentages may therefore exceed 100%. Which includes drinking den

attendants/service staff and salon workers, respondents with unclear or irregular income-generating

activities and registered clerical workers and respondents in well-paying jobs. Occupational categories were

collapsed into broader epidemiologically relevant groups to enhance interpretability and reduce

misclassification bias.

Prevalence of Skin-Bleaching Practice

The prevalence of skin-bleaching practice among respondents was 89.6%. Among users, 71.4% reported current use, while 12.5% reported past use. Only 10.4% reported never using skin-bleaching products.

Skin bleaching was more common among women aged 18–29 years (67.5%) compared with older age groups, indicating a strong age-related usage pattern.

Patterns of Skin-Bleaching Practices

Duration and Frequency of Use

Long-term exposure was common. Nearly three-quarters of users (72.5%) reported using skin-bleaching products for more than three years, while about one-quarter (24.7%) had used them for less than one year.

Frequent application was typical. Most users (64.2%) applied products once or twice daily, while 25% reported multiple daily applications. These patterns indicate high cumulative exposure potential.

Body Areas of Application

The most commonly treated body area was the face (98.2%), followed by arms (83.5%), legs (38.4%), and the entire body (28.5%). Facial use predominated, likely due to cultural emphasis on facial appearance and the higher cost of full-body product use. Application to visible body areas increases both cosmetic and toxicological relevance.

Types of Skin-Bleaching Products Used

Participants reported using multiple product types:

Soaps — 95.5%

Creams — 95%

Lotions — 93.4%

Serums — 84.2%

Oral tablets — 6%

Concurrent multi-product use was common (68.4%), indicating intentional product layering and increased cumulative exposure risk.

Sources and Motivations for Skin-Bleaching

Sources of Cosmetic Products

Skin-bleaching products were primarily obtained from informal sources:

Beauty salons — 97.3%

Informal street vendors — 88.6%

Local markets — 35.4%

Licensed shops or pharmacies — 23.1%

This distribution indicates a predominantly informal supply chain with limited regulatory oversight.

Motivations for Use Primary motivations included

Desire for lighter skin tone and perceived beauty enhancement — 97%

Media influence — 48.7%

Social or peer pressure — 38.5%

These findings confirm strong sociocultural drivers behind product use.

Self-Reported Health Effects

Dermatological Symptoms

A majority of users (67.2%) reported experiencing at least one dermatological adverse effect. Reported conditions included:

Skin thinning — 89.4%

Hyperpigmentation or dark spots — 56.5%

Acne or rashes — 23.3%

Skin irritation — 8.7%

Limited health literacy among some participants may reduce early recognition and care-seeking behavior.

Systemic Health Symptoms

Systemic symptoms were reported by 87% of users. Common complaints included:

Headaches — 92%

Fatigue — 90.4%

Menstrual irregularities — 67.5%

Urinary or kidney-related complaints — 35.2%

These symptom patterns are consistent with known toxicological effects of mercury and corticosteroid exposure, although causality cannot be confirmed due to the cross-sectional design.

Chemical Analysis of Cosmetic Samples

Nine cosmetic products (creams, lotions, soaps, and serums) were analyzed using ICP-OES for heavy metal content.

Heavy Metal Exceedance Rates

Mercury exceeded safety limits in 66.7% of samples

Lead exceeded limits in 33.3% of samples

Cadmium exceeded limits in 33.3% of samples

Risk categories were assigned based on comparison with international cosmetic safety limits:

Safe — at or below limit

Moderate — above limit up to twice the limit

High — more than twice the limit

Several serum and cream products fell into the high-risk category for mercury and lead.

Qualitative Label Findings

Label review identified several ingredients of toxicological concern, including hydroquinone, corticosteroids, glutathione, diethanolamine, formaldehyde, trichloroethylene, dibutyl phthalate, and p-phenylenediamine. These identifications were based solely on label claims and were not laboratory-verified. Many of these substances are restricted or prohibited under international cosmetic regulations.

Donabedian-Based Assessment

This study applied the Donabedian structure process outcome framework in accordance with WHO public health surveillance principles and Zanzibar Food and Drug Development Authority (ZFDA) cosmetic safety and regulatory guidelines. A mixed-methods approach was used. The structure domain assessed healthcare access, market characteristics, and regulatory capacity. Quantitative data evaluated access gaps, while laboratory screening of cosmetic products identified prohibited or restricted substances as defined by ZFDA and WHO. Qualitative interviews explored regulatory and enforcement challenges. The process domain examined exposure pathways. Surveys quantified prevalence, frequency, and duration of cosmetic use, and toxicological analysis linked use patterns with ingredient concentrations to estimate exposure intensity. Social drivers of use were explored qualitatively. The outcome domain assessed adverse health effects, chemical-specific toxicity linkages based on WHO risk thresholds, and psychosocial impacts. Findings were triangulated across domains to inform regulatory risk assessment and policy action

Qualitative results based on label claim

Qualitative review of product labels used by participants revealed the presence of several ingredients of toxicological concern, including hydroquinone, Corticosteroids, Glutathione, diethanolamine, trichloroethylene, and formaldehyde, which are either restricted or prohibited in cosmetic formulations. From facial scrab products they include formaldehyde, dibutyl phthalate, p-phenylenediamine, hydroxyphenol, ammonium persulfate, and ultraviolet filters such as oxybenzone and octinoxate. These ingredients were recorded based on product labeling and participant report only. No laboratory chemical analyses were conducted to verify the label claims therefore, results represent qualitative, label-claimed information. The detection of these substances based on label claims raises significant public health concerns, particularly given the frequent and prolonged use reported by participants. These substances are subject to strict regulatory controls or bans due to their potential dermatological, endocrine, and systemic toxicity

Discussion

This study documents a very high prevalence of skin-bleaching practices among women in Zanzibar, with nearly nine out of ten respondents reporting current or past use. The predominance of users among younger women indicates that skin-lightening practices are strongly embedded within contemporary sociocultural beauty norms and peer-influenced behavior patterns. Similar age-related trends have been reported in other Sub-Saharan African settings.

The sociodemographic profile of participants reflects socioeconomic vulnerability, characterized by low income, concentration in informal employment sectors, and modest educational attainment. These factors may contribute to both increased exposure risk and reduced access to reliable health information regarding cosmetic safety. Grouping occupations into broader epidemiological categories improved interpretability and strengthened associations between socioeconomic status and exposure patterns.

Usage patterns observed in this study indicate prolonged and intensive exposure. Most users reported more than three years of product use and frequent daily application, often multiple times per day. Facial and arm application predominated, involving areas with high cosmetic visibility and significant dermal absorption potential. Concurrent use of multiple products was common, suggesting intentional product layering that may amplify cumulative chemical exposure.

The supply chain for cosmetic products was largely informal, with most products obtained from beauty salons and street vendors rather than licensed pharmacies or regulated cosmetic outlets. This distribution pathway increases the likelihood that products bypass regulatory screening and quality control systems. Similar informal distribution patterns have been associated with higher rates of cosmetic non-compliance in other low- and middle-income settings.

Self-reported dermatological effects — particularly skin thinning, hyperpigmentation, acneiform reactions, and irritation — are consistent with known adverse effects of prolonged topical corticosteroid and hydroquinone exposure. The high prevalence of systemic symptoms, including headaches, fatigue, menstrual irregularities, and kidney-related complaints, aligns with established toxicological profiles of mercury and steroid exposure. Although causality cannot be established due to the cross-sectional design and reliance on self-reported symptoms, the consistency between reported symptoms and known toxic effects supports biological plausibility.

Laboratory analysis confirmed that a substantial proportion of sampled cosmetic products contained heavy metals above internationally recognized safety limits. Mercury exceedance was particularly frequent, followed by lead and cadmium. Chronic dermal exposure to these metals is associated with multisystem toxicity, including renal impairment, neurological dysfunction, immune effects, and reproductive risk. Because many users reported long-term and repeated application over large body surface areas, cumulative systemic absorption is a credible concern.

Qualitative label review further identified multiple restricted or prohibited ingredients, including hydroquinone, potent corticosteroids, formaldehyde-related compounds, and industrial solvents. Although label claims were not laboratory-verified for organic compounds, their declared presence raises regulatory and public health concerns, particularly when combined with high-frequency use patterns.

Environmental considerations are also relevant. Persistent cosmetic contaminants may enter wastewater and coastal ecosystems through washing and disposal. In small-island environments such as Zanzibar, where domestic effluents interface closely with marine systems, unsafe cosmetic ingredients may pose ecological as well as human health risks. This dimension supports the need for inter-agency collaboration between health and environmental authorities.

Donabedian Framework Interpretation

Using the Donabedian structure–process–outcome framework, the findings indicate that toxic cosmetic exposure is driven primarily by systemic weaknesses rather than individual behavior alone.

Structure factors include limited regulatory enforcement capacity, insufficient post-market surveillance, informal distribution channels, and constrained laboratory screening resources.

Process factors include high prevalence of use, prolonged duration, frequent application, multi-product layering, and strong sociocultural pressures promoting lighter skin tone.

Outcome factors include widespread dermatological complications, systemic symptom patterns consistent with toxic exposure, and potential reproductive and developmental risks.

This integrated interpretation supports the need for system-level public health and regulatory interventions.

Public Health and Policy Implications

Toxicological and Health Implications

The detection of elevated concentrations of mercury, lead, and cadmium in commonly used cosmetic products has important public health implications. These metals are associated with multisystem toxicity, particularly under chronic exposure conditions. Mercury is recognized as both a neurotoxin and nephrotoxin, lead exposure is linked to neurological and hematological effects, and cadmium is associated with renal and skeletal toxicity as well as carcinogenic potential.

Skin-bleaching practices typically involve repeated dermal application over extended periods and often over large body surface areas. Even when concentrations are near regulatory thresholds, chronic cumulative exposure may produce biologically meaningful toxic burden. The risk is especially relevant for women of reproductive age because certain metals can cross the placental barrier and may affect fetal development.

The widespread concurrent use of multiple cosmetic products further increases exposure potential through additive or interactive effects. From a preventive health perspective, reducing repeated long-term exposure represents a practical risk-reduction strategy.

Regulatory and Governance Implications

International cosmetic safety frameworks establish impurity limits and ingredient restrictions to protect consumers. The finding that several sampled products exceeded recommended heavy-metal limits and carried label-declared restricted substances suggests gaps in market surveillance and regulatory enforcement within informal cosmetic supply chains.

In the Zanzibar context, cosmetic oversight responsibilities fall under national regulatory authorities. Strengthening import control screening, product registration systems, and post-marketing surveillance would improve early detection of non-compliant products. Routine market sampling combined with laboratory verification can function as an effective preventive control measure.

Importantly, these findings should be interpreted at the system level rather than attributing responsibility to individual manufacturers or vendors. The public health priority is strengthening oversight systems and consumer protection mechanisms.

Public Health Practice Implications

From a public health practice perspective, several intervention areas emerge:

Laboratory SurveillanceRoutine screening of cosmetic products using validated analytical methods such as ICP-OES for metals and chromatographic methods for restricted organics would strengthen safety monitoring capacity.

Risk CommunicationTargeted consumer education campaigns are needed to increase awareness of potential risks associated with unregulated skin-bleaching products. Messaging should be culturally sensitive and avoid stigmatization.

Integration into Health ServicesCosmetic safety counseling can be incorporated into:

Maternal and reproductive health services

Community health outreach programs

Primary care and dermatology visits

Community EngagementCollaboration with community leaders, salon operators, and women’s groups can improve risk communication reach and acceptability.

Environmental Health Considerations

Cosmetic contaminants may also present environmental concerns. Persistent and bioactive compounds can enter wastewater systems through washing and disposal and may contribute to aquatic toxicity. In coastal and island ecosystems, the interface between domestic effluent and marine environments increases ecological sensitivity.

Strengthening coordination between health regulatory agencies and environmental authorities would support a more comprehensive risk-management approach.

Conclusion

This study provides integrated epidemiological and laboratory evidence indicating a high prevalence of skin-bleaching practices among women in Zanzibar and measurable exposure to potentially hazardous cosmetic ingredients. Frequent, prolonged, and multi-product use patterns were common, and most products were obtained through informal supply channels. Laboratory analysis demonstrated that a substantial proportion of sampled cosmetics contained heavy metals — particularly mercury — at concentrations exceeding internationally recognized safety limits, while label reviews identified several restricted or prohibited substances.

Self-reported dermatological and systemic symptoms among users were consistent with known toxicological effects of mercury, corticosteroids, and hydroquinone exposure, although causal relationships cannot be established due to the cross-sectional design. The convergence of high usage prevalence, elevated contaminant levels, and symptom patterns supports the presence of a meaningful public health concern.

Interpreted within the Donabedian structure–process–outcome framework, the findings indicate that toxic cosmetic exposure is primarily driven by systemic gaps in regulatory surveillance, market control, and consumer awareness rather than individual behavior alone. Strengthening cosmetic safety oversight, expanding laboratory monitoring capacity, and implementing culturally appropriate public health education are practical and preventive strategies for reducing avoidable exposure.

Positioning cosmetic safety as a public health priority — supported by regulatory strengthening, inter-agency collaboration, and community engagement — offers a feasible pathway to reduce chemical exposure risks and protect women’s reproductive and general health in Zanzibar and similar settings.