I had a patient ask me to re-run my column about warts. It's estimated that up to 12 percent of people worldwide have had warts and that 10-20 percent of school-aged children have them.

Warts are caused by a group of pesky viruses called human papilloma viruses or HPV. When people hear HPV they often think of the vaccine that can help prevent cervical cancer caused by certain strains of these viruses. There are over 100 known types of HPV, all of which share the characteristic of being able to infect skin.

Warts are spread by direct or indirect contact with another person who has them. They can also be spread from one location to another on the same person. They commonly attack areas where there is dry, cracked skin or open wounds. The incubation period from infection to development of a wart is usually 1-3 months, but it can take years.

The appearance of warts can vary from very flat lesions to large, raised ones. Larger warts are typically seen on the palms or soles of the feet. A "planter's wart" is common misnomer for a wart on the bottom of the foot. These warts have nothing to do with planting. The proper term is "plantar wart." Plantar is the anatomic term for the bottom surface of the foot. These warts usually appear to have a central core or seed, hence the term "seed wart." These "seeds" are actually small blood vessels containing blood clots.

Warts can be difficult to treat, and simple over the counter remedies often work just as well as medical treatments. Treatment success depends on the size and location of the wart as well as the aggressiveness of the treatment. Larger warts are usually covered by a protective callus that should be removed before applying treatment. Interestingly, 65 percent of warts may go away on their own within two years but a person always runs the risk of the wart spreading.

Home treatments can be 70 to 80 percent effective, but must be used consistently. Most home treatments involve acids such as salicylic acid (Compound-W®) that remove the top layers of the wart. Warts are constantly growing so any treatment needs to destroy wart tissue faster than it is growing.

More recently, home cryotherapy agents such as Compound-W Freeze Off® have become available. These work by freezing the wart tissue and destroying it. In my experience these treatments are not very effective, probably because they don't provide a deep enough freeze.

There are many home remedies that people swear by including applying pieces of raw garlic cloves or potatoes to the wart when sleeping. Putting duct tape on the warts is also felt to be helpful, but the scientific evidence is weak at best.

Doctors may use a number of different treatments for warts, but they rarely are any more effective than home treatments. If the patient has a limited number of warts, freezing with liquid nitrogen can be very effective but application can be painful. There are other acids, chemicals, acne medications and chemotherapy agents that can be applied topically. Some doctors make their own blend of medications or home remedies. Sometimes injections are also given in or around the wart to stimulate the immune system to kill the HPV. As a last resort, laser destruction or surgical removal may be used. Any treatment is more effective if it is applied when the warts are small.