Psoriasis is a chronic skin condition resulting from an accelerated life cycle of skin cells. Normally, skin cells shed after about a month, but with psoriasis, this process is dramatically sped up to just a few days. This rapid turnover leads to a buildup of cells on the skin’s surface, forming the characteristic raised, scaly patches, or plaques. The core concern of “spreading” the condition by scratching addresses a common fear, but the answer is clear: psoriasis is not an infection and cannot be transmitted.
Psoriasis is Not Contagious
Psoriasis is fundamentally an immune-mediated disorder, not a communicable disease. It is caused by the immune system mistakenly signaling skin cells to grow too quickly, an internal mechanism driven by genetics and environmental factors. Specifically, a type of white blood cell called a T-cell becomes overactive and triggers an inflammatory response in the skin.
This internal dysfunction sharply contrasts with infections caused by external pathogens. Consequently, you cannot acquire psoriasis from another person through casual contact, such as touching a plaque, sharing a towel, or swimming in the same pool. The disease clustering in families is due to a shared genetic predisposition, not contagion.
How Physical Injury Causes New Lesions (The Koebner Phenomenon)
Although psoriasis is not contagious, scratching can indeed cause new lesions to appear, which is often misinterpreted as “spreading.” This process is known as the Koebner phenomenon, or the isomorphic response, and occurs in an estimated 25 to 30% of people with psoriasis. The Koebner phenomenon describes how a physical trauma to previously healthy skin can trigger the formation of a new psoriatic plaque in that exact location.
The trauma can be relatively minor and includes scratching, rubbing, sunburn, insect bites, vaccinations, or surgical incisions. When the skin is injured, the localized trauma initiates an inflammatory cascade that recruits inflammatory cells and mediators to the site. These recruited cells, including T-cells and mast cells, release chemical signals such as interleukins, which drive the rapid skin cell production characteristic of psoriasis.
The appearance of the new lesion is not immediate; it is a localized immune reaction that takes time to develop. New plaques typically appear in the traumatized area between 10 and 20 days after the injury. This mechanism is the activation of the underlying autoimmune disease process by a physical trigger, not the spread of an infectious agent.
Strategies for Managing Itching
The intense itching associated with psoriasis is a major factor that contributes to the Koebner phenomenon, as scratching is a form of skin trauma. Breaking the itch-scratch cycle is therefore a practical way to minimize the formation of new lesions in unaffected areas.
- Daily moisturizing is a simple yet effective strategy, as it locks water into the skin, reducing the dryness and scaling that often cause the sensation of itch. Heavier ointments or creams are generally more effective than lotions at sealing in moisture, particularly when applied right after bathing.
- Non-prescription products containing ingredients like menthol, camphor, or calamine can provide temporary relief by creating a cooling or numbing sensation on the skin.
- Soaking in a warm bath with added colloidal oatmeal or Epsom salts for about 10 minutes can also help to soothe irritated skin and soften scales.
- Keeping fingernails trimmed short is another behavioral modification that can minimize damage and reduce the severity of trauma if scratching does occur.
- Applying a cool, damp washcloth or compress to an itchy area can help calm the nerve signals that transmit the sensation of itch to the brain.