Wilkerson and Wilkin,1 following Pathak et al,2 question the depigmenting effect of azelaic acid on pigmented guinea pig skin, point out the difficulty of assessing its efficacy on hyperpigmented disorders in comparison with the quinone class of drugs, and find it difficult to accept that azelaic acid affects only hyperproliferative cells with no effect on normal cells in culture.
With regard to the first point, as we pointed out in our comments3 on the article by Pathak et al,2 we have always emphasized that azelaic acid does not cause depigmentation in normal skin of whatever color, animal or human; that its mode of action is different from that of the quinone class of drugs, which can depigment hypermelanosis as well as normal skin; and that, therefore, it cannot be regarded as a "depigmenting agent" in the commonly accepted meaning of the term. In view of this,
Nazzaro-Porro M, Passi S, Zina G, Breathnach AS. The Depigmenting Effect of Azelaic Acid. Arch Dermatol. 1990;126(12):1649-1650. doi:10.1001/archderm.1990.01670360117026