Last winter I had a psoriasis flare up myself, and here are two things I did to help reduce it under my doctor's advice:
1. In the winter there is less sunlight, which means you get less vitamin D which helps the treatment of psoriasis. My doctor said even though I take a multi-vitamin, it wasn't enough vitamin D. She suggested I add a vitamin D supplement as well, which really helped me.
2. Stress level. I was going through a lot of stressful things in my life last winter, which definitely contributed to my psoriasis. The stress of the holidays, the loss of sunlight, personal problems, all of these things can make your psoriasis worse. Try out some things to reduce your stress level such as journaling, doing some exercise such as yoga, or doing a meditation exercise.
Here are some other recommended tricks to deal with psoriasis:
3. Hot showers can irritate skin. Try to keep your shower as short as possible and with luke warm water. Don't give in to the urge to looah and exfoliate, instead use products that are meant for sensitive skin. Don't shower more than once a day.
4. Moisturizing really helps. If you moisturize after the shower, it helps seal in moisture, relieving itchy skin. Slathering on petroleum jelly is best, but it can be a bit greasy and messy. If you are uncomfortable with using petroleum jelly, a good compromise may be to use a petroleum based lotion, such as Vaseline's Intensive Rescue lotions.
5. If you are taking any medication for your psorasis, check with your doctor to make sure that they are sufficient for the winter time.
6. Consider phototherapy to give you the extra sunlight you need. It can be done in a doctor's office or even in the comfort of your own home. Have some extra money? A vacation in the middle of the winter in a sunny, tropical locale can do your skin wonders!
And remember, it's always best to consult with your doctor first before trying any suggested treatments.