Boric acid is applied in a very dilute eyewash solution. Dilute boric acid can be used as a vaginal douche to treat bacterial vaginitis due to excessive alkalinity, as well as non-albicans candidiasis. As an antibacterial compound, boric acid can also be used as an acne treatment. It is also used to prevent athlete's foot by introducing dust into socks. Various preparations can be used to treat certain types of otitis externa (ear infection) in both humans and animals.[20] The preservative in UK urine sample bottles is boric acid.
Boric acid solutions used to wash the eyes or on abraded skin are known to be toxic, particularly to infants, especially after repeated use. This is due to the slow elimination rate.