This is an article which is in response to a BBC reader/watcher’s question about why her fingernails are turning green. In a situation like this, ALWAYS go see your doctor. This is probably a fungal infection, but you need to be seen by a doctor. No questions asked. Go.
BBC – Health – Ask the doctor – Fingernails – green
If your nails are getting very soggy from being in damp conditions, then the natural defences of the nail become weak and more easily breached by fungi or even moulds. These are present throughout the environment but normally can’t penetrate the barriers of the body’s immune defence system.
However the usual picture is for infection to start away from the nail bed, rather than in the bed or base of the nail as in your case, and to then cause a brittle, distorted, creamy/grey/yellow nail. The fungal infection (known as onychomycosis) is usually caused by the same sort of fungus which causes ringworm in the skin (mostly a group known as the dermatophytes).
Onychomycosis is common and often accompanies a fungal infection elsewhere in the body. It’s very difficult to cure – you’ll need to take antifungal tablets for at least six weeks to get high doses into the growing nail until the infection has grown out (although there’s a new treatment which is in the form of a nail varnish which you paint on).