Absorption of products following topical use
| AGENT | ABSORPTION |
|---|---|
| Benzoyl peroxide | Not detected in serum. Small amounts of the metabolite benzoate are absorbed and easily eliminated2,3 |
| Tretinoin | Endogenous vitamin A levels remained unchanged after repeated applications of 0.05% tretinoin4 |
| Clindamycin phosphate | Not detected in plasma5 |
| Erythromycin | Not detectable in serum6 |
| Salicylic acid | Undetectable from up to 25% in normal skin (depends on vehicle, pH, strength, and quantity applied). Levels might be higher when applied to damaged skin7 |
| Glycolic acid | Up to 27% is absorbed into the skin, dependent on pH, concentration, and time8 |
| Hydroquinone | 35%–45.3% is systemically absorbed through the skin9 |
| Sunscreens (oxybenzone, octocrylene, octisalate) | Below the limit of detection up to 8.7%10,11 |
| Dihydroxyacetone (self-tanning) | Estimated at 0.5% systemically available12 |
| Depilatory products | |
| • Thioglycolic acid | Human studies on systemic absorption of thioglycolic acid have not been conducted |
| • Sodium, calcium, and potassium hydroxide | The amount found in consumer products, which would come in contact with skin, would be negligible compared with daily dietary intakes of these ions and therefore would not increase serum levels13 |
| Hydrogen peroxide (skin bleaching) | In an in vitro study involving human skin, hydrogen peroxide was detectable in the dermis only after the application of high hydrogen peroxide concentrations for several hours14 |