**Background:** Skin-lightening cosmetics are widely used globally, particularly in Nigeria where a WHO survey reported 77% of women use them. These products often contain hazardous substances such as hydroquinone, mercury (Hg), and arsenic (As), which are associated with serious health effects including carcinoma, ochronosis, neurological damage, renal impairment, and developmental toxicity. Despite bans or restrictions in many countries, these chemicals remain prevalent in unregulated cosmetics. This study aimed to assess the levels of hydroquinone, Hg, and As in skin-lightening cosmetics marketed in Ilorin, Nigeria, an area not previously studied for these contaminants.
**Methods:** Ten skin-lightening cosmetic samples (labeled A–K) were randomly purchased from outlets across three local government areas in Ilorin (Ilorin South, Central, and North). Hydroquinone was identified by TLC (n-hexane/acetone 60:40) and quantified using a validated UV-spectrophotometric method at 290 nm. The method showed excellent linearity (r²=0.9993) over 5–50 µg/mL, with LOD 0.75 µg/mL, LOQ 2.28 µg/mL, %RSD 0.01–0.35%, and recovery 95.85–103.56%. Mercury was determined by cold vapour atomic absorption spectrophotometry (AAS) at 253.7 nm (LOD 0.5 µg/L, LOQ 1.65 µg/L, r²=0.9983). Arsenic was analyzed by hydride generation AAS at 193.7 nm (LOD 1.0 µg/L, LOQ 3.3 µg/L, r²=0.9991). Samples were digested with HNO₃/HClO₄ (2:1) at 105°C. All analyses were performed in triplicate.
**Key Results:** All ten samples contained hydroquinone, mercury, and arsenic. Hydroquinone concentrations ranged from 1.9% to 3.3% w/w. Only samples A (2.0%), D (1.9%), and H (2.0%) were within the WHO permissible limit of 2% w/w. The remaining seven samples (B, C, E, F, G, I, J) exceeded this limit, with values from 2.1% to 3.3% w/w. Mercury levels ranged from 0.08 to 2.52 µg/g; samples A (2.52 µg/g), C (2.10 µg/g), and D (1.80 µg/g) exceeded the FDA/WHO limit of 1 µg/g. Arsenic concentrations ranged from 0.07 to 5.30 µg/g, with samples F (5.30 µg/g) and H (2.68 µg/g) showing notably high levels. Only six of ten products had NAFDAC registration numbers; none listed mercury or arsenic on labels, and only four mentioned hydroquinone. Most products were imported from Côte d'Ivoire (54.6%) and Togo (27.3%).
**Clinical Implications:** The widespread presence of hydroquinone above permissible limits in 70% of samples raises concerns about ochronosis, dermatitis, and potential carcinogenicity with prolonged use. Mercury levels exceeding safety thresholds in 30% of samples pose risks of nephrotoxicity, neurotoxicity, and developmental harm, especially in pregnant women. The high arsenic content in two samples (5.30 and 2.68 µg/g) is alarming given its association with skin cancer, neuropathy, and systemic toxicity. The lack of ingredient disclosure and NAFDAC registration for many products indicates poor regulatory enforcement. These findings underscore the urgent need for routine quality surveillance, stricter import controls, and public awareness campaigns to mitigate health risks from unregulated skin-lightening cosmetics in Nigeria.