It is possible that an exogenously administered drug/cosmetic might potentiate the adverse effects of laser treatment. This could happen in at least two ways: (i) drug/cosmetic absorbs light from the laser, becomes activated resulting in a phototoxicological event; and, (ii) drug/ cosmetic changes the structure/function of the skin. A third possibility falls into the category of unknown, which may be populated with anecdotal reports without any mechanistic basis.
There are few, if any, reports of a phototoxicological response at the wavelengths of the lasers in question (600-1200 nm) outside of intentional photodynamic therapy. This is related to the absorption profile of chemicals where the majority of photosensitizers are activated by more energetic short wavelengths falling in the UVA (320-400 nm) region [170-172], and to a lesser extent UVB (290-320 nm). In short, a direct phototoxicological response is unlikely if not negligible, since current drugs/cosmetics do not absorb wavelengths emitted by nonablative visible/IR lasers.
The second possible contraindication related to photosensitivity is the change in structure and function of the skin produced by a drug or cosmetic which might impart enhanced sensitivity to laser light. For example, treatment of severe acne with isotretinoin has been reported to result in keloid formation and reduce wound healing following laser treatment [173]. This increased skin sensitivity is consistent with the effects of isotretinoin and other retinoic acid derivatives on skin. This potential interaction is of concern as female patients with androgen profiles including severe acne and hirsutism have a tendency to coexist. Khatri [174] followed 7 patients undergoing isotretinoin therapy treated with diode laser for hair removal. In this study, patients showed mild erythema after laser treatment, but no erythema, pigmentary change, swelling, or scarring at any of the follow-up visits. Cassano et al. [175] reported similar findings in 6 patients treated with diode laser, 4 subjects undergoing isotretinoin therapy, and the remaining 2 who had just completed isotretinoin therapy. These studies, while limited, demonstrate the safety of diode laser hair removal in patients undergoing isotretinoin therapy. Whereas these data should not be applied to all lasers, patients using isotretinoin can be safety treated.