Dermatology/large white marks on toenails
Mr. Mark wrote at 2013-08-16 13:30:41
Looks like a fungus to me as well. If left untreated it will spread into the white half-moon (part of the living nail known as the Matrix.) There the fungus can cause thickening and deformity of the nail by damaging the living cells of the nail both chemically and physically. The damage can be irreversible. Please seek medical help to find out what it is.