Xeroderma pigmentosum (XP) is a rare genetic disease with eight known subtypes. XP affects one out of every 250,000 people worldwide. In the United States and Europe, one out of every one million people have XP.

The condition is more common in Japan, North Africa, and the Middle East than in the United States or Europe. It’s typically diagnosed in infancy or early childhood. It can also be diagnosed prenatally, or before birth. It’s less common to be diagnosed in late childhood or early adulthood.

People with XP experience extreme sensitivity to UV light (photosensitivity). This sensitivity makes it impossible to be out in the sun. Some people with XP also experience certain neurological conditions like intellectual disabilities, developmental delays, or hearing loss. Eye problems are also common.

XP symptoms typically start to show during infancy or within the first three years of life. Some people with the disease begin showing symptoms in late childhood or early adulthood.

Skin

Babies and toddlers with the disease usually start to freckle on areas exposed to the sun. These areas include:

  • face
  • neck
  • arms
  • legs

Painful, blistering sunburns can also occur. This happens regardless of how much time is spent in the sun. In some cases, children start to sunburn immediately upon exposure to the sun. These sunburns may result in redness and blistering that can last for weeks.

Extreme changes in pigmentation are common. This can result in patches of skin becoming much darker (hyperpigmentation). Or the skin can lose its natural color and become pale pink or white (hypopigmentation).

Other symptoms may also start to appear during childhood. These include:

Check out: What’s wrong with my skin? 38 causes of discolored skin patches »

Vision and hearing

People with XP often experience symptoms affecting the eyes. These include:

  • extreme sensitivity to light (photophobia)
  • eyelids that turn abnormally inward (entropion) or outward (ectropion)
  • cloudiness of the eye lens
  • inflammation of the corneas, eyelid lining, and the white part of the eye (sclera)
  • excessive tear production
  • blindness caused by lesions close to the eye

Some people may also experience progressive hearing loss that may lead to complete hearing loss.

Neurological

Some types of XP, such as De Sanctis-Cacchione syndrome, are associated with dwarfism, mental deficiency, hypogonadism, and other neurological issues.

Neurological symptoms of De Sanctis-Cacchione syndrome and some XP subtypes can include:

  • slow or no reflexes
  • poor motor skills
  • small head size (microcephaly)
  • developmental delays
  • muscle rigidity, spasticity, or weakness
  • poor control of bodily movement (ataxia)

XP is an inherited disorder. Each subtype is caused by a mutation in a different gene. Every type of XP is marked by the gene’s inability to repair, or replicate, DNA that has been damaged by UV light.

Even though the genes affected vary from type to type, extreme sensitivity to sunlight is always clear. Painful sunburns, and later skin cancer if skin isn’t protected, always result.

Seven of the eight known types of XP are categorized as autosomal recessive conditions. This means that both parents of the person with XP were carriers of the mutated gene, but didn’t have the disease themselves.

One form, XP dominant type, is an autosomal dominant condition. In XP dominant type, only one parent had a defective gene. The parent may also have the disease, as opposed to being a carrier.

There are several other conditions characterized by extreme photosensitivity and the inability of specific genes to repair DNA damage to the body. If you have XP, you may also be diagnosed with one of these disorders:

  • trichothiodystrophy
  • Bloom syndrome
  • Neill-Dingwall or Cockayne syndrome

XP is a hereditary disease. The only people at risk are those who have a parent, or parents, who either have the disease, or are carriers of the disease.

XP is more prevalent in certain isolated, geographic areas. This may, in part, be caused by consanguinity. This means that both parents are blood relatives, such as cousins. If parents share a genetic background, their chances of passing XP on to their children increase.

The most common complications of XP are skin cancer, neurologic abnormalities, and eye abnormalities.

Malignancies are also common. Repeated surgeries to remove tumors can result in disfigurement, but can be avoided by taking precautions against sun exposure.

Those with XP need to take extreme measures to protect every surface of the body from UV light at all times. These precautions include:

  • wearing protective clothing, such as long sleeve tops, pants, and wide-brimmed hats
  • applying broad spectrum sunscreen
  • using UV-absorbing glasses with shields

Learn more: What does melanoma look like? »

Because XP is rare, and photosensitivity may be caused by many other conditions, doctors typically don’t test for it.

If you or your child starts to display symptoms, your doctor will rule out other conditions first. If you suspect XP, keeping a symptom diary can help you to get a diagnosis and the support you need.

If you have a family history of XP, your doctor can determine your carrier status through a screening that uses a blood or saliva sample.

If you’re pregnant and want to determine your fetus’s risk of XP, a test called amniocentesis can be done. This test analyzes the fluid surrounding the fetus. It can determine if the fetus has XP and other genetic diseases.

If XP is suspected, your doctor will use a variety of diagnostic tools to determine if you have it and what type you may have.

These tools include:

  • assessment of your family history
  • physical examination
  • symptom analysis
  • genetic testing

After a diagnosis, getting regular checkups for precancerous growths (actinic keratosis) is very important. This can help to reduce the incidence of skin cancer and end the need for more invasive surgeries.

There isn’t a cure for XP, but its symptoms can be managed. Staying out of the sun and avoiding other UV light sources is crucial. This means slathering up with sunscreen and covering up completely whenever going out of doors.

While indoors, avoid window seats and light fixtures that emit UV light. For example, halogen lamps emit higher levels of UV light. UV meters can determine if artificial light sources in your home, school, or work emit UV light. Steps can then be taken to change out light sources or continue extreme photoprotection even while inside.

XP can be life-threatening if protective measures aren’t taken to avoid UV light. This means limiting your amount of sun exposure and always protecting your skin and eyes when outside.

XP can be an isolating disease. It can be hard for children to attend school or other activities. You can help by letting other people, like teachers and family members, know about your child’s condition. Together, you can work to create an active life for your child.

There are night camps, like Camp Sundown, that bring kids with photosensitivity together in a joyful setting. Some community spaces like parks, gyms, swimming pools, and other recreational areas remain open after dark.

Acknowledging the emotional and physical aspects of XP is also important.

If you or your child has XP, it will be important for you to create a lifestyle that centers around avoiding sun exposure. This doesn’t mean you have to stop going outdoors during daytime hours, but it does mean setting realistic expectations for outdoor activities.

Sunlight can also pass through windows. Using window shades, or window protection film, can help filter out harmful UV rays.

Cigarette smoke can exacerbate skin damage and should be avoided.

Preventing skin cancer and protecting the eyes are key. This means using full-spectrum sun screen at all times and covering up the skin with clothing. There are UV ray-resistant clothes manufactured for this purpose. Sunglasses and wide brimmed hats can also help to shield the eyes from damaging light.

Routine skin and eye exams can help in identifying and removing precancerous growths before damage is done. This may help reduce your risk for skin cancer.