Wart

• 1. Introduction

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  Warts are small, rough, non-cancerous growths, and most people will have one at some point in their lives. Estimates put the rate of non-genital warts in the general population somewhere between 1 and 13 percent. They turn up more often in young people. Some look like a cauliflower, and others like a solid blister. They usually appear on the hands and feet, though the face and genitals can be affected too. A person may have a single wart or many at once. Something this ordinary has puzzled physicians for centuries. It has also inspired elaborate folk rituals on both sides of the Atlantic. What exactly are these growths, and what sets them apart from cancer? Why did the real cause stay hidden for so long? And what actually makes them go away?

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• 2. Seven Kinds of Growth

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  A raised bump with a roughened surface, most often on the hand, is the common wart, formally called verruca vulgaris. It can grow anywhere on the body. Some people know it as a palmer wart or a junior wart. Flat warts, or verruca plana, look nothing like it. They are small, smooth and flesh-coloured, they can appear in large numbers, and they favour the face, neck, hands, wrists and knees.

  Near the eyelids and lips, a thread-like or finger-like form called the filiform or digitate wart is most common. Around the fingernails, warts can gather into a cauliflower-like cluster known as a periungual wart. On the soles of the feet, the plantar wart, or verruca plantaris, forms a hard and sometimes painful lump. It often has several black specks at its centre. It sits mainly on pressure points and between the toes. When plantar-type warts crowd tightly together, usually on the soles or the hands, doctors call the group a mosaic wart.

  Genital warts have several names, including venereal wart, condyloma acuminatum and verruca acuminata. As the name suggests, they occur on the genitalia, and they are often sexually transmitted.

  Each shape tends to follow a particular virus. Common warts are most often tied to human papillomavirus types 2 and 4, and plantar warts to type 1. Flat warts involve types 3, 10 and 28. Genital warts come mostly from types 6 and 11. A condition called Heck's disease, or focal epithelial hyperplasia, involves types 13 and 32. Those numbers point to a virus family far larger than most people imagine.

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• 3. The Virus Behind It

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  Roughly 130 types of human papillomavirus, or HPV, are known to science. Warts are only one thing they do. The virus infects a tissue called the squamous epithelium, usually in the skin or the genitals. Each type can generally manage only a few specific areas of the body. Many produce a benign growth that doctors call a wart or a papilloma.

  A sharp line divides the family in two. Low-risk types are the ones associated with warts and similar conditions. High-risk types, including 16 and 18, are associated with cancers, notably cervical cancer. They can also cause some vulvar, vaginal, penile, anal and oropharyngeal cancers. Other high-risk types on the list include 31, 33, 35, 39, 45, 52, 58 and 59.

  The virus is believed to get in through a break in the skin. That fits the known risk factors: public showers and pools, work with meat, eczema, and a weakened immune system. One variety is even named after a trade. HPV type 7 is the cause of butcher's warts.

  Under a microscope, a common wart has a distinctive signature. The outer layer of skin, the stratum corneum, is thickened, a change called hyperkeratosis. The stratum spinosum and the stratum granulosum thicken too. The ridges of tissue beneath, called rete ridges, grow longer, and large blood vessels sit where the two main skin layers meet. Through a dermatoscope, warts commonly show fingerlike or knoblike extensions.

  None of this was known to the physicians who first tried to explain warts.

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• 4. Searching for the Cause

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  Hippocrates, who lived from about 460 to about 370 BC, described warts, and surviving ancient medical texts show they were a documented disease by his time. The Roman physician Aulus Cornelius Celsus, who lived from about 25 BC to about 50 AD, went further in his book De Medecia. He described different types. One was myrmecia, today recognized as the plantar wart. He also counted the acrochordon, or skin tag, as a wart.

  In the 13th century, the surgeons William of Saliceto and Lanfranc of Milan described warts in their books. The word verruca came later. The physician Daniel Sennert introduced it in his 1636 book Hypomnemata physicae.

  What caused warts remained a fight inside the profession. In the early 18th century, the physician Daniel Turner, who published the first book on dermatology, proposed that damaged nerves close to the skin were responsible. In the mid-18th century, the surgeon John Hunter popularized a different idea, that warts came from a syphilis infection. The surgeon Benjamin Bell showed that warts were caused by a disease entirely unrelated to syphilis. He also established a causal link between warts and cancer. In the 19th century, the chief physician of Verona Hospital tied warts to cervical cancer in particular.

  Still, in 1874 the dermatologist Ferdinand Ritter von Hebra observed that the "influences causing warts are still very obscure".

  The breakthrough came in 1907, when the physician Giuseppe Ciuffo first showed that a viral infection causes warts. In 1976, the virologist Harald zur Hausen became the first to discover that the culprit was the human papillomavirus. His continuing research built the evidence needed to develop an HPV vaccine, which first became available in 2006.

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• 5. Vaccines and a Hardy Virus

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  Gardasil is designed to block infection by HPV types 16, 18, 6 and 11. It was first aimed at cervical cancers and genital warts. Types 16 and 18 cause about 70 percent of cervical cancer cases, along with some vulvar, vaginal, penile and anal cancers. Types 6 and 11 are responsible for 90 percent of documented genital warts. Before the vaccine was widely adopted, an estimated 12 percent of sexually active women had genital warts.

  A later version, Gardasil 9, protects against nine types: 6, 11, 16, 18, 31, 33, 45, 52 and 58. Neither vaccine currently protects against the strains behind plantar warts, the verrucae.

  The virus itself is stubborn. It is relatively hardy and shrugs off many common disinfectants. It also resists drying and heat. Only a few things reliably kill it. These include 90 percent ethanol for at least a minute, 2 percent glutaraldehyde, 30 percent chlorhexidine, and 1 percent sodium hypochlorite. Temperatures of 100 C and ultraviolet radiation also destroy it.

  Everyday habits count as prevention too. Wearing shoes outdoors helps, as does avoiding unsanitized places without proper footwear or clothing, such as public restrooms and locker rooms. For genital warts, barrier methods such as condoms reduce the risk. Careful handling of needles and sharp objects guards against skin injuries that could let the virus in.

  When prevention fails, one plain acid sits at the top of the list of remedies.

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• 6. Medicines and Chemicals

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  A review of wart treatments reached a clear verdict on salicylic acid: topical products containing it beat a placebo. Over-the-counter versions come in two main forms. One is an adhesive pad treated with the acid, and the other is a bottled solution of salicylic and lactic acid. A dermatologist can prescribe a higher concentration than the shelf versions carry.

  Harder cases call for stronger agents. Fluorouracil cream, a chemotherapy agent sometimes used on skin cancer, can be tried on especially resistant warts. It works by blocking the virus from making and repairing its DNA and RNA. Imiquimod cream helps the immune system fight the virus by encouraging interferon production, and the U.S. Food and Drug Administration has approved it for genital warts. Cantharidin occurs naturally in many beetles of the family Meloidae and raises blisters on the skin. It is not FDA approved, but it can be obtained through Canada or certain compounding pharmacies in the United States.

  Bleomycin, a more potent chemotherapy drug, can be injected into deep warts, usually in one or two injections. It is not FDA approved for this use, and side effects include necrosis of the digits, nail loss and Raynaud syndrome. Dinitrochlorobenzene, applied directly to the wart, shows a cure rate of 80 percent in studies. Because it is known to cause genetic mutations, a physician must administer it. It works by provoking an allergic reaction, and the resulting inflammation drives off the virus. Cidofovir, an antiviral, is injected into HPV lesions in the larynx as an experimental treatment.

  Other options include Verrutop, an acid and metal-ion solution that produces nitrites, which denature viral proteins and mummify the wart without damaging surrounding skin. A silver nitrate caustic pencil is sold over the counter too. In a placebo-controlled study of 70 patients, nine days of silver nitrate cleared all warts in 43 percent, against 11 percent for placebo. Trichloroacetic acid is a fallback when salicylic acid or freezing fails, applied about once a week and prone to burning and stinging.

  Some treatments skip chemistry and go straight to extremes of temperature and light.

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• 7. Freezing, Burning and Taping

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  Liquid nitrogen is the usual tool of cryotherapy, which appears about as effective as salicylic acid, though fewer trials have tested it. The freeze raises a blister between the wart and the layer of skin beneath. The wart and the surrounding dead skin then fall off. Warts on thin skin need an average of three to four treatments. Plantar warts, on calloused skin, can take dozens or more.

  Lasers work differently. A pulse dye laser, at a wavelength of 582 nanometres, is absorbed by hemoglobin in blood cells. It is gentler and more likely to heal without scarring, and it needs no local anaesthetic or sedation. Typically it takes 2 to 4 treatments, 10-14 days apart, though extreme cases need many more. A carbon dioxide laser is absorbed by water and vaporizes tissue, so it requires a local anaesthetic. An infrared coagulator follows the same principle with an intense beam of infrared light. It costs less, but like the laser it can cause blistering, pain and scarring.

  Other procedures include electrodesiccation, microwave treatment, surgical curettage and keratolysis, the removal of dead surface skin, often by paring with a pumice stone or blade. Injecting proteins from candida, the MMR vaccine or tuberculin into the wart appears safe and effective.

  Then there is duct tape, laid over the wart. How it might work is still unknown, and trials have left the evidence inconclusive. Yet its simplicity and few side effects make some researchers reluctant to dismiss it. Doing nothing is also a legitimate choice, since most warts disappear on their own within months to years.

  The oldest remedies of all never involved a clinic.

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• 8. Toads, Stump Water and Folklore

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  Greater celandine, Chelidonium majus, produces an acrid yellow latex, and daily application of it is a traditional treatment. Folk belief offers stranger cures. In English folk belief, touching toads gives you warts. In German belief, touching a toad under a full moon cures them. The common toads of the Northern Hemisphere do have glands that protrude from the skin and superficially resemble warts. Toads do not carry the virus.

  Mark Twain wrote such remedies into The Adventures of Tom Sawyer. Tom proposes spunk-water, also called stump-water, which collects in the hollow of a tree stump. One puts a hand in at midnight and recites a charm. Then comes the hard part. You "walk away quick, eleven steps, with your eyes shut", turn around three times, and walk home without speaking to anybody. Speak, and "the charm's busted". Huckleberry Finn has a remedy involving a dead cat thrown into a graveyard as a devil comes to collect a wicked person recently buried.

  Another remedy in the same spirit calls for splitting a bean, drawing blood from the wart, and pressing a half of the bean to it. The half is then buried at a crossroads at midnight, on the theory that the blood will draw the wart away. Twain is recognized as an early collector and recorder of genuine American folklore.

  Similar practices turn up elsewhere. In Louisiana, one cure has the sufferer rub the wart with a potato and bury it. When the buried potato dries up, the wart will be cured. In Northern Ireland, water from one particular well on Rathlin Island is credited with the power to cure warts.

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