Psoriasis is a chronic autoimmune condition where the immune system mistakenly triggers an accelerated life cycle of skin cells, causing them to build up rapidly on the skin’s surface. This process results in the characteristic thick, scaly, and often itchy patches known as plaques. While psoriasis is not contagious, physical injury to the skin, including aggressive scratching, can directly cause new patches to form. This localized reaction is a known phenomenon that people with a genetic predisposition to psoriasis must understand.
How Injury Triggers New Psoriasis Patches
The appearance of new psoriatic plaques at the site of skin trauma is known in dermatology as the Koebner phenomenon, or isomorphic response. This reaction can be triggered by various forms of injury, such as cuts, scrapes, sunburn, surgical incisions, and the micro-trauma caused by persistent scratching. The Koebner phenomenon is estimated to occur in approximately 25% to 30% of people with psoriasis.
When the skin is injured, it initiates an inflammatory cascade as part of the body’s healing process. In people with psoriasis, this trauma acts as a trigger in genetically predisposed skin, leading to the recruitment and activation of specific immune cells. These immune cells, including T-cells, release inflammatory signaling molecules called cytokines at the injury site.
This intense, localized inflammatory response stimulates the keratinocytes, which are the main cells in the outer layer of the skin, to proliferate excessively. Instead of the typical 28-day turnover cycle, these cells begin to reproduce within just a few days. This rapid cell turnover results in the formation of a new psoriatic plaque, often appearing in the linear shape of the original scratch or injury.
Managing the Urge to Scratch and Prevent Trauma
Minimizing skin trauma is a practical way to reduce the risk of triggering the Koebner phenomenon. Managing the itch-scratch cycle begins with a consistent moisturizing routine. Applying a heavy ointment or cream immediately after bathing helps lock moisture into the skin, which reduces dryness and subsequent irritation.
Over-the-counter anti-itch products containing menthol or camphor can help soothe the skin, but a dermatologist may recommend prescription topical treatments.
To manage intense itching and prevent inadvertent trauma, several measures can be taken:
- Substitute scratching with a gentler alternative, such as patting or pinching the itchy area.
- Apply a cool, damp cloth or ice pack for temporary relief by numbing nerve endings.
- Keep fingernails trimmed short.
- Wear soft cotton gloves at night to serve as a physical barrier.
Psoriasis is Not Contagious: Addressing Misconceptions
Psoriasis is an autoimmune disorder, meaning it stems from a dysfunction within the body’s own immune system, not from an outside pathogen. It is not caused by a virus, bacteria, or fungus. It is important to distinguish this from the localized spread caused by trauma.
Psoriasis cannot be transmitted through casual contact, such as touching, hugging, or shaking hands with someone who has the condition. Sharing towels, using public swimming pools, or being in close proximity to a person with plaques poses no risk of transmission. The condition is driven by a combination of genetic factors and immune system activity.
The scaly appearance of psoriatic plaques often leads to the false belief that the condition is contagious. Educating others about the non-infectious nature of psoriasis is necessary to reduce stigma and anxiety surrounding the disorder.