According to the National Psoriasis Foundation, psoriasis is not a contagious condition. People cannot catch it from other people, and the psoriasis lesions are not infectious.
Normal skin cells grow slowly and flake off after about four weeks, states WebMD. In skin with psoriasis, new skin cells grow uncontrollably and rapidly, often in days rather than weeks. This causes the skin cells to build up and form thick patches called plaques. Plaques can be small or large. They often appear on the elbows, knees, scalp, hands, feet or back. While most common in adults, children and teens may also develop psoriasis.