Warts are small growths on the skin that affect almost all people at some point during their lives, explains the Merck Manual for Healthcare Professionals. Skin warts can affect people of all ages and may appear singly or in the hundreds. Infections with any of the more than 100 types of the human papilloma virus, or HPV, can cause skin warts.
Common Warts
Infections with HPV types 1, 2, 4, 27 and 29 can cause common warts, notes the Merck Manual. Common warts tend to appear mainly on the hands, but they may occur on the skin anywhere on the body, explains the University of Maryland Medical Center. The warts usually do not cause any symptoms, but they might occasionally cause pain. They appear as small knob-like growths--or nodules--and can be yellow, brown or gray in color. Some variations of common warts may have a cauliflower shape; these appear most commonly on the head and neck. Transmission of the types of HPV that cause common warts occurs with direct contact between people. Transmission can also occur through contact with surfaces touched by a person with warts, note the health professionals at the Mayo Clinic. It can take up to 6 months for common warts to appear after the initial infection with the virus that causes the warts.
Plantar Warts
HPV1 causes plantar warts, which appear on the soles of the feet, notes the Merck Manual. This virus also causes palmar warts that appear on the palms. Plantar warts can be tender and cause discomfort during standing or walking. The HPV 1 virus flourishes in damp, warm locations such as the floors of showers, and though not highly contagious, it can pass between people who come into contact with such surfaces after a person with warts has touched them. Scratching a wart can lead to transmission of the virus to other parts of the foot, notes the Mayo Clinic. Transmission can also occur through contact with skin or blood that comes from a wart. Due to different immune system reactions, only some who contact the virus will develop warts, and the act of sharing showers with an infected person will not necessarily cause warts.
Genital Warts
HPV 6 and HPV 11 cause more than 90 percent of external genital warts, according to the Merck Manual. Genital warts can affect the skin and the mucus membranes on the inner linings of the genitals and anus. Transmission the HPV 6 and HPV 11 occurs through sexual contact, including digital and oral contact with the infected area. Approximately 6 million new infections occur every year in the U.S., notes Merck.
