The darkening of the skin after using retinoic acid to wipe flat warts on the hands is a normal adverse drug reaction, usually after stopping the drug, to avoid the blackened skin by friction, this pigmentation will gradually diminish or even disappear on its own. Vitamin A cream is commonly used in clinical practice to treat acne vulgaris, especially blackheads and pimples lesions, senile, solar or drug atrophy of the skin, ichthyosis and a variety of keratosis pilaris and hyperpigmentation of the skin, psoriasis, but the external use of this product may cause skin irritation symptoms, such as burning sensation, erythema and desquamation, and even hyperpigmentation, so that the skin blackened and so on the adverse reactions. Usually these adverse reactions will gradually diminish or even disappear after discontinuing the use of retinoic acid cream. It should be noted that the black pigmentation will be aggravated if it is often rubbed, and it is recommended that patients should pay attention to avoid repeated rubbing of the skin.