It is used extensively for athletes foot --a  50% solution is suggested. 

Fungus around the finger nail and toenails --try tea tea oil

 To start a treatment it is important to test the tea tree oil first for reaction. If it is used clean an area and prepare it for a localized herbal salve treatment, it can be used as; 30%, 50 % up to 100% solution but use a a bit of cotton ball [or what have you] carefully or twist it on the end of a tooth pick and carefully wipe only the small area that is to be treated.Try one trouble spot at a time. What you put on the skin goes in to the body. Try tea tree oil with pure water -- 1 part tea tree oil to 3 parts water. For instance 5 drops tea tree oil to 15 parts [drops] water. Experiment with amounts tea tree oil verses water until you find what works for you.

There is a possibility of side effect of dermatitis developing [ rash, redness and/or burning develops, discontinue use and it will disappear]. Try a small amount in a small area first. [ Inside of the elbow is suggested as a test site.] Add more water, it will still work.