We've all seen these toenails - the thickened, yellow ones - and you may even have one or more yourself.

Fungus in the toenails can be a frustrating problem. It's caused by the athlete's foot fungus getting into the nails. Once it's in the nails, it's often joined by yeasts or moulds making it even harder to clear.

Three things to remember. If you have athlete's foot, get it cleared up pronto so you don't end up with a nail problem. If you have an early nail infection, meaning the nail is discolored but not thickened, see your doctor for Penlac, the clear, prescription nail polish. It may work. If you have a more advanced case, you'll need a prescription for oral medication so see your dermatologist or primary care doc.

There are a few other problems like psoriasis and lichen planus that can cause nail problems, so see your doctor!

See Dr. Irwin's new in-depth article on Acne Scars and Other Scars