This invention relates to a topical composition for treating amino acid based substrates comprising a protected thiol compound having the formula R—(S—Pr)m where R is a functional group, S is sulfur, and Pr is a heterocyclic protecting group, and m is an integer between 1 and 100. The invention further relates to systems which comprise this protected thiol compound and an activating mechanism. The protected thiol compounds of the present invention may be used in hair care compositions, textile care compositions, cosmetic compositions, oral care compositions, skin care, nail care, laundry care, acne care and animal care compositions. Preferred embodiments of the present invention provide a modified UV absorber and a modified antioxidant, methods for making them and compositions conprising them.