Here's some info from netdoctor HTH
Warts and verrucas
Dr John Pillinger, GP
What are warts?
Warts can be transmitted indirectly, especially via hard floors like those found in swimming pools.
Warts are caused by a viral infection in the skin. Ordinary warts on the hands and feet are caused by viruses, which only affect humans. More than 60 different viruses that cause warts are known.
Warts are rarely seen on children under the age of three, but after this age they become more frequent. Among children between four and six, 5 to 10 per cent get warts, while 15 to 20 per cent of children between the ages of 16 and 18 have them. The frequency drops drastically again on reaching adulthood.
What do warts look like?
Warts on the hands are found most frequently around the nails and on the fingers.
They are shaped like a cauliflower.
What do verrucas look like?
Verrucas are seen most commonly where the ball of the foot is exposed to pressure.
They are often sore to touch and to stand or walk on.
Verrucas appear as areas of flat, thicker skin with a harder edge around a softer centre.
On closer examination, small black spots can be seen in the verruca. These are not - as some people believe - roots in the warts. The black spots are caused by bleeding in the verruca as a result of standing and walking on it.
Are warts and verrucas contagious?
The wart virus is very contagious. The skin cells on the warts release thousands of viruses and touching the wart or skin cells on it releases the virus, which can then infect others.
Some children often have trouble not scratching or biting warts on their hands, which can cause the warts to bleed and break up, making then more contagious.
The risk of infection is reduced if one paints the warts with nail polish. Warts may also infect indirectly, especially from hard floors, for example in bathrooms and swimming pools.
A foot with verrucas releases virus infected cells onto the floor. The wet and more receptive skin of others may then become infected.
People with scratches or cuts on the soles of their feet are especially vulnerable.
Not all people are susceptible to the virus. When children share bathrooms that contain wart viruses, some of them will get verrucas, while others seem to be totally immune. The reason for this difference is not known.
It can take several months for warts and verrucas to develop after infection.
How are warts and verrucas treated?
There is no treatment that is guaranteed to remove warts or verrucas. Most go away by themselves within one or two years, and this fact may be why many folk remedies seem to work almost miraculously.
The treatment of warts and verrucas depends on the person's age, how many there are, where they are, and what trouble they cause. Especially with children, the option of treatment should be set against the relatively good chances of a spontaneous cure.
It may be necessary to try more than one different kind of treatment before the warts or verrucas go away.
There are a number of over-the-counter medicines available from your local pharmacist to treat warts and verrucas. The pharmacist will advise you on how to use each medicine and the precautions required.
The doctor may treat them with corrosive solutions together with liquid plaster. After this treatment it is necessary to pare down the treated area with a pumice stone or emery board.
The doctor can also freeze warts and verrucas away with liquid nitrogen. Often several freezing treatments will be necessary before the warts are totally removed.