Phosphoric Acid is not automatically unsafe for seborrheic dermatitis, but its concentration and the finished product's pH matter. In cosmetics it is mainly used in small amounts to adjust or stabilise pH, not as an exfoliating treatment.

The exact-name seb derm search found an unrelated chemical stability paper, and no applicable Malassezia evidence was found. Proper formulation matters because concentrated acid can irritate, while the ingredient list does not reveal the final pH. Stop using a product that repeatedly stings or reddens affected skin.