For some people with psoriasis, even the tiniest pinprick or a bite from a mosquito can trigger plaques to appear in new places. Anytime your skin is hurt or irritated, you can get a new patch of psoriasis. Doctors call this reaction the Koebner phenomenon, and it happens to 1 out of 4 people who have psoriasis. Heinrich Koebner, a dermatologist from the 19th century, first defined the condition. Doctors sometimes call it “isomorphic response” or “Koebnerization.” It happens most often in people with psoriasis, but it happens in other skin conditions, too, including warts and vitiligo. If you have active flares, you are more likely to have a Koebner response. But it can still happen even if you have never had plaques on your skin. Each reaction has its own pace. It takes about 10-20 days after a skin injury for plaques to show up. Sometimes it can take as long as 2 years. Doctors aren’t sure what makes your skin respond to an injury with plaques. You can have a Koebner response from anything that changes your skin on the outside or the inside, including: You can also trigger the condition when you get a tattoo, vaccinations, or acupuncture. Even everyday activities like shaving can cause a flare. The weather plays a role, too. It happens more often during cold winter months and less often in warm summer months. Koebner phenomenon plaques are just like regular psoriasis flare-ups. They can be: They can also crack and bleed. In most cases, more severe injuries mean more plaques. Unlike regular psoriasis flares that show up on knees, elbows, the scalp, and the lower back, Koebner phenomenon plaques can happen anywhere your skin has been hurt. This is the idea some scientists have that an injury can also trigger psoriatic arthritis. With this type of Koebner response if you already have psoriasis and you injure a bone or joint, you’re 30% more likely to get psoriatic arthritis in that spot. As soon as you see new plaques show up after a skin injury, tell your doctor. They can add this information to your treatment plan. Knowing what triggers your psoriasis can help you avoid flares in the future. Koebner phenomenon plaques get the same treatment as your regular psoriasis plaques. There are many options, including: Psoriasis treatments work differently for different people. Your doctor can help you find the one that works best for you. The best way to keep it at bay is to take the same precautions you usually do with psoriasis: