Agents used for tanning with astringent properties have been used for hyperhidrosis.[58,148] These agents denature keratin proteins in the stratum corneum layer lining the sweat pore, which leads to a superficial closure of the pore that lasts several days, until reparative desquamation of the cell layer occurs. Acids and aldehydes such as formaldehyde, glutaraldehyde, tannic acid, and trichloroacetic acid have all been used to treat hyperhidrosis. These agents are now essentially considered obsolete, although low concentrations of astringents may be found in some commercial preparations.
Formaldehyde induces contact sensitivity, leading to allergic contact dermatitis in 15% to 20% of patients. Methenamine, used systemically as a urinary tract antiseptic, releases formaldehyde in the presence of acid. Methenamine, contained in several commercial products, has been successfully used as a topical agent for hyperhidrosis by slowly releasing formaldehyde in the presence of acid eccrine sweat.[15,58] Patients using commercially prepared stick antiperspirant with 5% methenamine had a significant improvement in palmoplantar sweating (P<0.001) and no development of allergic contact sensitization. In another study, 24 of 26 patients had decreased palmar and plantar sweating with use of the 5% methenamine stick; one patient with prior allergic contact dermatitis due to formaldehyde had no reaction to methenamine.
Glutaraldehyde is another tanning agent that has been used to treat hyperhidrosis. Patients who are sensitized to formaldehyde did not react to glutaraldehyde. A 10% glutaraldehyde solution decreased sweating on the soles of all 25 patients treated, but had no clinical effect on axillary hyperhidrosis. Yellow-brown discoloration occurs in the skin with use of glutaraldehyde, and thus it may only be clinically useful on the soles. Tannic acid is less effective than glutaraldehyde and can also cause skin discoloration.