Unlike contagious diseases that you can catch from another person, experts believe that psoriasis is caused by a genetic vulnerability and triggered by a set of environmental factors. To reduce your risk of flare-ups, the National Psoriasis Foundation recommends steering clear of the following psoriasis triggers:

1. Stress. It's a common conundrum for many psoriasis patients: Stress can lead to flare-ups, but living with psoriasis can be very stressful. To reduce the stressors in your life, try relaxation techniques, ask your friends and family for help, and seek out a psoriasis support group.

2. Skin injury or trauma. In some people, trauma can lead to flare-ups at the injury site or elsewhere, a condition known as Koebner's phenomenon. As such, it's best to minimize your exposure to activities that could cause burns, cuts, bruises, scratches, or sunburns, and to avoid tattoos completely.

3. Some medications. Certain medications, such as lithium, some beta-blockers, malaria drugs, and nonsteroidal anti-inflammatory drugs (NSAIDs), are known to trigger psoriasis flare-ups. Be sure to talk to your doctor about the risks and the possibility of alternative treatments.

4. Infections. Some conditions, such as strep throat, tonsillitis, and HIV, can trigger psoriasis symptoms or make them worse. In these cases, the result is most often guttate, a form of psoriasis that produces small, red spots, usually on the trunk and limbs. Again, talk to your doctor about ways to reduce your disease risk.

5. Cold, dry weather. Because cold, dry weather can dry out the skin, it can trigger or exacerbate flare-ups. In contrast, warm, humid weather appears to help control outbreaks. Although you can't change the weather outside, you can improve your indoor environment by keeping the temperature at a comfortably warm level and investing in a humidifier.