Folate deficiency - patients with severe psoriasis have a risk of developing folate deficiency. Folate is a B vitamin that is vital for proper nerve function; it also prevents birth defects. Folate also prevents high levels of homocysteine, which increase the risk of heart disease.

Heart problems, obesity and diabetes - a higher percentage of individuals with psoriasis develop heart problems, diabetes and/or obesity. Experts do not know whether there is a genetic link between these conditions and psoriasis. People with moderate-severe psoriasis, ideally should be tested for these conditions. Experts from UC Davis explained in Archives of Dermatology that fat cells in patients with psoriasis secrete cytokines that raise insulin resistance in the liver and muscle, which initiates the destruction of the insulin-producing beta cells in the pancreas.
Bad body temperature regulation - patients with erythrodermic psoriasis may have abnormalities in the body’s ability to control temperature.

Zumbusch psoriasis - this is a combination of erythrodermic and pustular psoriasis. The condition may develop suddenly. The patient may experience fever, chills, muscle weakness and weight loss. Sometimes there may be an over-accumulation of fluids, protein loss, and electrolyte imbalances; in such cases the patient may need to be hospitalized until fluid, chemical balances and body temperature are normalized. Zumbusch psoriasis is especially dangerous if the patient is elderly.
Psoriatic arthritis - in the majority of cases, psoriatic arthritis symptoms are mild. 

However, the following complications are possible:

Arthritis mutilans - an extremely severe form of chronic rheumatoid arthritis, in which the bones are reabsorbed, resulting in the collapse of soft tissue. When the hands are affected it can cause a phenomenon called telescoping fingers; the feet may also be affected. Patients with other arthritic conditions, such as osteoarthritis or rheumatoid arthritis in the joints of the fingers have a higher risk.

Risk of developing psoriatic arthritis - it is estimated that between 10% and 20% of all patients with psoriasis develop psoriatic arthritis; in about 20% of these people the arthritis symptoms occur before the psoriasis ones.
Cancers - patients with severe psoriasis who received systemic medications (those that affect the whole body) have a higher risk of developing skin cancers and lymphomas.

Psychological and emotional consequences - living with psoriasis often has emotional and social consequences.
Patients may feel embarrassed by having visible plaques and that can lead to depression. In some cases the individual may withdraw from society.

Symptoms may become so severe that patients have to leave their jobs, further increasing the risk of psychological and emotional problems.
Several surveys have shown that a significant number of patients with psoriasis report a negative mental and physical impact that is similar to several chronic conditions, including cancer, hypertension, heart disease, depression and diabetes.

According to a national survey (USA) Psoriasis Uncovered of people with the most severe form of psoriasis:

20% say that their psoriasis contributed towards the loss of a job or resignation.
25% believe that their psoriasis has caused an intimate relationship to end.
43% said psoriasis had prevented them from making new friends.
83% expressed dissatisfaction with their current treatment.

The majority of GPs (general practitioners, primary care physicians), specialists and other health care professionals know and understand that psoriasis has an emotional and psychological impact. It is important that the patient discusses any concerns and anxiety they may have.