The Koebner phenomenon is when a skin disorder, such as psoriasis, vitiligo, or lichen planus, occurs at the site of an injury on the skin.
It may occur in people with an existing skin condition or a person without previous skin problems.
However, the likelihood of a person experiencing the Koebner phenomenon depends more on the individual rather than the type of injury they have.
A person who reacts after one type of injury, such as a cut, may have a higher chance of developing a Koebner response after another kind of injury, such as a burn or bite.
Some people develop Koebner phenomenon lesions within 10–20 days after a skin injury, but symptoms can appear from 3 days to 2 years after the event.
Doctors are not sure exactly why the Koebner phenomenon happens.
Researchers have suggested that various factors might play a role, including the:
- immune system
- vascular system
- neural system
In psoriasis, the result may be due to a chain reaction involving various systems.
Some possible triggers include:
- contact with allergens or irritants
- cuts or scrapes
- insect stings, bites, burns, or other trauma to the skin
- exposure to radiation or sunburn
When an injury occurs, or an unwanted substance enters the body, the immune system launches an inflammatory response as part of the process of dealing with the problem.
The Koebner phenomenon is also more common in people who received a diagnosis of psoriasis when they were very young.
Some people may experience the phenomenon after having a vaccination or tattoo.
How can having a tattoo affect psoriasis? Learn more here.
The Koebner phenomenon is more common in people with psoriasis and other skin disorders, although not everyone with psoriasis will experience it.
Some experts believe that the Koebner phenomenon is more likely to occur during a psoriasis flare, and it may be more extensive after a severe injury.
In people with psoriasis, the Koebner phenomenon results in psoriasis plaques in or around the injured area. The patches may be linear or follow the shape of a cut, blister, or insect bite.
Sometimes, it is not possible for a person to avoid a cut or scrape. However, people can take some measures to reduce the risk. These include avoiding:
Getting sunburned: Use sunscreen, stay in the shade, or wear sun protective clothes that cover the body.
Contact with irritants: Products ranging from beauty treatments to household chemicals can irritate the skin.
Scratching: Use topical treatments during a psoriasis flare to reduce itching.
Injuries and bites: Wear clothes that cover the body when gardening, camping, and so on.
Rubbing the skin: When bathing or showering, use products that a doctor recommends. Use lukewarm water, wash gently with the palms of the hands, and pat the skin dry after bathing. Avoid abrasive substances and sponges and try not to rub the skin.
A person should seek medical help if:
- a skin change occurs without an apparent cause and in a new location
- a linear patch forms around the site of a recent injury
If the new patch takes months or years to develop, it may be hard to identify the cause.
A doctor will carry out a physical examination and look for:
- a linear patch or lesion at the site of a cut or scrape
- a patch that resembles psoriasis (or another skin disorder)
- a patch that is not due to the normal progress of the disease, an infection, or another cause
Learn more here about how to recognize the symptoms of different types of psoriasis.
Treatment for the Koebner phenomenon depends on the underlying condition.
In the case of psoriasis, treatment options may include:
- topical treatments, such as medicated creams and ointments
- light therapy
- oral medications
For certain types of psoriasis or moderate to severe symptoms, a doctor may prescribe a type of drug known as a biologic. This relatively new class of drugs targets specific parts of the immune system and appears to be effective at reducing the risk of a flare and the severity of symptoms.
Once a Koebner phenomenon lesion appears after one particular type of injury or cut, a person may experience it again after another injury, whatever the cause.
A person who experiences the Koebner phenomenon should take some extra precautions if their work or daily activity puts them at a higher risk of getting a cut or scrape.
For people with psoriasis, a doctor will probably recommend the same treatment as for the other psoriasis plaques. Sometimes, a doctor may recommend additional treatment options.