Fitzpatrick skin types 4-6 do not respond well to which of the following?

Fitzpatrick skin types 4 to 6 have higher melanin content, which provides them with increased protection against UV radiation but also makes them more prone to complications from certain aggressive treatments. TCA, or trichloroacetic acid, is a strong chemical peel that exfoliates the skin and removes damaged skin layers.

This type of peel can lead to post-inflammatory hyperpigmentation or scarring in individuals with darker skin types. Hence, the use of TCA on these skin types requires caution, and it is generally not well tolerated due to the risk of adverse reactions.

In contrast, retinol, salicylic acid, and glycolic acid, while they should still be used judiciously, can be adjusted in concentration and formulation to be more suitable for these skin types. They can typically help with skin concerns like acne and uneven texture without the same level of risk that TCA presents.