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A variety of factors -- ranging from emotional stress and trauma to streptococcal infection -- can cause an episode of psoriasis. Recent research indicates that some abnormality in the immune system is the key cause of psoriasis.
Why does my psoriasis get worse in the winter? A combination of dry air, decreased sunlight exposure, and colder temperatures can all contribute to winter psoriasis flares. Frequent moisturizing and use of a home humidifier can help alleviate some of the symptoms.