There is no known cause of psoriasis. However, doctors have discovered several factors that can contribute to the development of psoriasis:

Family History

Experts believe that psoriasis has genetic traits that can be passed down. About one in three people with psoriasis have a relative with the disease, according to the National Psoriasis Foundation. A parent with the disease has about a 10 percent chance of passing it down to a child, where two parents with psoriasis have about a 50 percent chance of passing down the trait.

Stress

While stress doesn’t cause psoriasis, it is a major factor in its development and often the cause of severe outbreaks.

Tobacco

A study published in Psoriasis Advance states that cigarette smoking nearly doubles a person’s chance of acquiring psoriasis and is higher in women. Other studies have shown that people who smoke and have psoriasis develop more aggressive symptoms, namely in their extremities.

Alcohol

Research into the effects of alcohol on psoriasis is a bit muddled because smoking and drinking often go hand-in-hand. Still, researchers believe alcohol can worsen symptoms because it upsets the liver and may trigger the growth of Candida, a type of yeast that can worsen psoriasis symptoms.

Cold Temperatures

Those with psoriasis in colder climates know that winter is typically when symptoms get worse. The extreme cold and dryness of winter weather pulls moisture from the skin, inflaming psoriasis symptoms.

Race

People with fairer complexions, such as Caucasians, are typically more likely to develop psoriasis than darker-complexioned races.

Medications

Certain medications, such as steroid-based ones and those used to treat malaria, can increase a person’s chance of developing psoriasis.

Viral and Bacterial Infections

Psoriasis may be more severe in patients who have a compromised immune system. This includes people who have AIDS, are undergoing chemotherapy treatments for cancer, or have another autoimmune disorder, such as lupus or Celiac disease. Children and young adults with recurring infections, such as strep throat or upper respiratory infection, are also at an increased risk.

Obesity

Inverse psoriasis is most common in people who are overweight. This is due to the fact that inverse psoriasis is exacerbated by the friction and sweating that occurs in deep skin folds.

Again, none of these will cause psoriasis, but they will increase the likelihood of developing the disease, or worsen the symptoms.