I have had this problem for some time, likely gotten from my folks that have both had it for some time. The bottom surface of the toenail becomes soft and expands to many times its normal size, pushing the remaining hard (but very brittle) top of the nail away. Essentially, the nail is separated from the skin beneath it. It can be painful if you catch it on something that pulls up on your nail since the only thing holding it on is aroudn the cuticle. My solution was to cut it as far back as possible. Over many years, it is spreading to my other toenails as well. It's an usightly thing. The dermatologists/doctors that I and my folks have visited over the years pretty much all say you have to take an internal medication (essentially a fungicide) that grows into the nail as it grows out, killing the fungus. The bad thing about this type of medication is that it is very hard on your liver, since the liver tries to break down and convert such foreign chemicals in your body. That is the main reason the treatment has to be capped at about 12 weeks. Both my parents tried this but it didn't completely get rid of it within that window of time and the fungus resumed its previous state after several months. I'm not too keen on a treatment for a largely (to me) cosmetic problem that could cause semi-permanent damage to my liver.
If these topical treatments are as good as you guys claim, I'll all for giving it a try. My unsightly toenails' current state doesn't bother me physically, but after all this time I'm quite tired of having to look at them. I also don't like being a potential infector to anyone else.