Psoriasis is a chronic, inflammatory disease of the immune system. It is characterized by red, scaly, itchy patches of skin usually on the knees. elbows, scalp and torso but can develop anywhere on the body. It often appears between the ages of 15 and 35, but about 10 to 15 percent of those with psoriasis first developed it under the age of 10. 
Link to Physical Conditions
In recent years, psoriasis has been linked to other, serious medical conditions:
Diabetes - A study released in 2012 showed that those with psoriasis are twice as likely to develop type 2 diabetes as those without psoriasis. Researchers looked at results from 27 different studies, finding that all but one of those studies found a link between psoriasis and type 2 diabetes. April Armstrong, lead author of the study explains, "There is evidence that fat cells in psoriasis patients may not function normally. These cells secrete inflammatory substances known as cytokines that increase insulin resistance in the liver and muscle and initiate destruction of insulin-producing cells in the pancreas." 
High Blood Pressure - Several studies have linked psoriasis with high blood pressure. The World Health Organization (WHO) recently recommended that healthcare professionals "routinely scan for the health condition." 
Obesity - Researchers at Landspitali University Hospital looked at over 6,500 people and found that, of those with psoriasis, 63 percent had abdominal stomach obesity and 44 percent had high triglyceride levels. Only 13 percent of those with psoriasis did not show any evidence of the metabolic syndrome elements of obesity, high blood pressure, diabetes, and high cholesterol and triglyceride levels. 
Arthritis - Around 10 percent of patients with psoriasis also develop arthritis, with severe cases of the skin disease, this number rises with arthritis being 3 to 4 times more common than in those without psoriasis. Usually, the psoriasis develops before the arthritis. 
Cardiovascular disease - According to Medical News Today, severe psoriasis has been linked to "major cardiovascular events, such as heart attacks."  Additionally, the risks associated with obesity can contribute to cardiovascular disease, putting those with psoriasis at a higher risk for developing it.
Psoriasis and Mental Health
In addition to the increased risk to some serious physical illnesses, those with psoriasis have a higher risk of developing depression, anxiety and having suicidal thoughts. The link isn't completely understood, however, the association between depression and psoriasis has been suggested since back in the 1960s. Since then, studies have shown that there is a correlation and the more severe the psoriasis, the higher the risk of developing depression or anxiety. Treating and managing the psoriasis has been found to improve the mental health issues.
"Frequently Asked Questions," Date Unknown, Staff Writer, National Psoriasis Foundation
"Psoriasis and Obesity Linked," 2010, Dec. 21, Sy Kraft, Medical News Today
 "Psoriasis Increases Risk of High Blood Pressure," 2013, APril 11, Kelly Fitzgerald, Medical News Today
"Psoriasis Linked to Higher Depression, Anxiety and Suicidal Feelings Risk," 2010, Aug 16, Christian Nordqvist, Medical News Today
 "Psoriasis Patients Twice as Likely to Develop Diabetes," 2012, Oct. 16, Kelly Fitzgerald, Medical News Today
  "Psoriasis Patients Urged to Be Aware of Links With Serious Diseases," 2012, Mar 20, Catharien Paddock, Ph.D., Medical News Today