Hydroquinone is used clinically as a topical depigmenting agent for conditions such as chloasma and melasma, and it is used cosmetically as a skin-whitening agent. It has been estimated that 35% to 45% is systemically absorbed following topical use in humans. A single study has been published involving the use of hydroquinone during pregnancy with no increase in adverse events; however, the sample size of pregnant women was small. Based on available data, hydroquinone use during pregnancy does not appear to be associated with an increased risk of major malformations or other adverse effects. However, because of substantial absorption compared with other products, it is best to minimize exposure until further studies can confirm safety.
Sunscreens are commonly used to protect the skin from the sun’s harmful rays. They have been found to cause little toxicity in animals and have very limited dermal or systemic absorption. Sunscreens have also been used in pregnancy to treat or prevent melasma; adverse events have not been reported.
Dihydroxyacetone is a color additive found in self-tanning products to produce an artificial tan. Color develops following topical application owing to dihydroxyacetone binding to amino acids in the stratum corneum. These products contain dihydroxyacetone in concentrations ranging from 1% to 15%, and when applied topically, systemic levels are minimal (0.5%); therefore, use during pregnancy would not be of concern.
Various topical agents, such as depilatory and hair-bleaching creams, are available to address issues of hair removal or reduce the appearance of hair. According to Health Canada guidelines, thioglycolic acid is permitted in depilatory products at concentrations equal to or less than 5% with a pH of 7 to 12.7.
Sodium, calcium, and potassium hydroxide, also found in depilatory creams, disassociates into sodium, calcium, potassium, and hydroxide ions. These ions are found abundantly in the body, and the amount of these chemicals in consumer products that come in contact with skin would be negligible, especially compared with the average daily dietary intake. In addition, although they might permeate the skin, the systemic absorption of these ions is minimal. Therefore, they do not increase serum levels and would not be considered a problem for use during pregnancy.
In an in vitro study involving human skin, hydrogen peroxide was detectable in the dermis only after applying high hydrogen peroxide concentrations for several hours. However, because cosmetic products such as hair-bleaching creams contain low concentrations of hydrogen peroxide, substantial amounts are unlikely to be absorbed after topical application. In addition, once absorbed, hydrogen peroxide is rapidly metabolized. Therefore, using these products during pregnancy is not expected to be a concern when done in moderation.
Retinol peels should be avoided during pregnancy. (See Topical Retinoids). Glycolic acid and Salicylic acid peels are generally considered safe. Avoid salicylic acid peels on rare occasions applied over a large surface area (40% or more of the body's surface area).