# Spreading of Dangerous Skin-Lightening Products as a Result of Colourism: A Review
## 3 Toxic Ingredients in Skin Lightening Cosmetics  
_Mercury_  
The main sources of mercury exposure in the past were industries (such as felt hat factories) and the composition and subsequent intake of mercury-based medicines. The use of mercury-containing skin-lightening products is currently a major cause of chronic mercury poisoning in some areas of the world [20]; despite their limited effectiveness, toxicity and the fact that they are banned in many countries, these products are still available and widely used worldwide. They can be found in a range of creams, milks, lotions, gels, oils and soaps. Mercury occurs in three forms: elemental (or metallic) mercury (Hg\({}^{0}\)), inorganic mercury compounds (existing in two oxidative states: mercurous, Hg\({}^{+}\), and mercuric, Hg\({}^{++}\)) and organic mercury compounds. Inorganic mercury (mercurous chloride or calomel, Hg\({}_{2}\)Cl\({}_{2}\); ammoniated mercury, HgNH\({}_{2}\)Cl; mercuric iodide, HgI\({}_{2}\); mercurous oxide, Hg\({}_{2}\)O; mercuric chloride, HgCl\({}_{2}\)) is the one commonly found in skin-lightening preparations [21], although methylmercury has recently been reported to be present in a skin-lightening product in the United States [22]. Mercury compounds suppress melanin production in skin melanocytes. Tyrosine, a type III copper protein, plays a key role in the synthesis of this pigment because, as already mentioned, it catalyses the first two reactions of melanin production: the hydroxylation of the amino acid L-tyrosinease to DOPA and then the conversion of DOPA to dopaquinone. Mercurous and mercuric ions inhibit melanin synthesis by competing with copper in tyrosinase; in particular, they bind to the His residue of the catalytic centre of the enzyme. This inhibition is irreversible [23]. Humans are exposed to mercury through dermal absorption, inhalation of elemental mercury vapours (especially in cases of long-term exposure) and ingestion. Inorganicmercury salts contained in creams and other cosme are easily absorbed through the skin; they penetrate the epidermis and are also absorbed through sweat glands, sebaceous glands and hair follicles [24], through which Hg eventually accumulates in the hair of the scalp [25]. [PERSON] et al. [25] studied Hg exposure in students using cosme to lighten their skin and found that Hg concentrations in the hair had a statistically significant correlation with the Hg concentration in cosmetics. Dermal absorption depends on factors such as mercury concentration, frequency of product application, skin integrity, lipophilicity of the vehicle in the cosmetic product and the hydration of the stratum corneum; ingestion of mercury can occur after topical application around the mouth and hand-to-mouth contact [26]. Inorganic mercury compounds accumulate in the body's organs, with the highest concentration found in the kidney, near the proximal tubule; urinary excretion is the main route of elimination [24]. Since inorganic mercury compounds are not lipophilic, they do not readily pass through the blood-placenta or the blood-brain barriers [24]; however, prolonged dermal exposure can lead to accumulation in the central nervous system and neurotoxicity [27]. Inorganic mercury salts are mainly excreted in urine and faeces; high levels of urinary mercury are frequently associated with the use of mercury-containing skin listeners. According to current information on exposure to cosmetics for commonly used products (1.22 g for a face cream and 4.42 g for a body lotion; [28]), a consumer using a cosmetic containing 10,000 ppm mercury could absorb up to 450 ug in a single application [29]. Increased and often elevated concentrations of mercury in urine have been found in people who used skin-lightening products and also in family members who were not using them [27; 30; 31]. The inhalation of elemental mercury vapours depends on the transformation of inorganic mercury compounds into elemental mercury, which can occur in the presence of low pH and UV radiation [32; 33].