Boric Acid

Boric acid is used primarily as a mild antiseptic/buffering agent, typically at low concentrations in personal care, but it can irritate skin and especially eyes and mucous membranes, with stinging more likely on compromised barriers (eczema, post-procedure). Human experience and safety assessments note irritation potential that is dose- and exposure-dependent, so in sensitive-skin routines and leave-on contexts a patch test is prudent. Given the non-negligible irritation risk in reactive individuals and the need for caution on damaged skin, it fits a moderate irritancy score. Safety Notes: In modern OTC skincare/cosmetic products, boric acid is most often used at very low levels (about 0.01–0.5%) as a pH-adjuster/buffering or mild antimicrobial support ingredient in leave-on creams/lotions and some rinse-off cleansers, with traces down to ~0.01% appearing in broader preservative/buffer systems. At the high end of consumer-available products, boric acid is found in stronger antiseptic/astringent and anti-odor topical preparations (often marketed for skin irritation/rashes or hygiene) where 2–5% is observed; concentrations above this are uncommon in mainstream OTC cosmetics and more associated with medicinal/professional uses rather than typical cosmetic leave-on formulations.