Psoriasis is a non-contagious skin disease that affects almost 10 million people across North America. About 500,000 people are living with psoriasis in Canada. Psoriasis usually appears between the ages of 15 and 35 and the average age at diagnosis is 28, but people of any age can be affected.
In the most common form of psoriasis, plaque psoriasis, certain areas of the skin develop red patches of various sizes, covered with dry, silvery scales. The skin lesions can be painful and itchy. Inflammation will come and go for people with psoriasis, and presently there is no known cure.
Doctors don't know what causes psoriasis. However, they do know that the certain cells of the immune system known as T-cells are involved in the inflammation. One theory is that the T-cells are triggered and become overactive in psoriasis. It is suspected that there's a genetic element; however, psoriasis can appear in children who have no family history of the disease. It is estimated that there is a 10% chance of a person developing psoriasis if they have one parent with the condition and a 30% chance if both parents are affected. This compares with a 2% to 4% incidence of psoriasis in the general population.
The process of inflammation is less of a mystery. Normally, skin cells reproduce just fast enough to replace dying cells on the surface, so that there is always about the same number of skin layers. However, when the skin is wounded, cells go into overdrive. Cells reproduce much faster, and extra blood is pumped to the site to help with wound healing. The result is redness and inflammation.
In psoriasis, undamaged skin goes into the wound-repair cycle. New cells appear and push their way to the surface faster than they can be shed. The extra cells create a raised area. The cells on top receive no blood. They quickly die to form the scaly white crust associated with psoriasis lesions. What is normally a 28- to 30-day process to shed and replace skin cells takes only 3 to 5 days in psoriasis.
Sometimes, psoriasis flare-ups can be provoked by external triggers. Possible triggers of flare-ups include:
The typical psoriasis lesion is a sharply defined red area covered in white or silvery scales. This is plaque psoriasis, the most common form of the disease. The knees, elbows, scalp, trunk, and outer sides of the arms and legs are the areas most frequently affected.
Guttate psoriasis gets its name from Latin for "drops," because the lesions are often teardrop-shaped. When a flare-up is provoked by illness or medication, it's often guttate in form. Guttate lesions usually occur on the trunk, arms, and legs.
Inverse psoriasis is particularly painful. Normally, psoriasis affects the skin around the outside of joints. Inverse psoriasis affects the folds of the skin – the armpits, for example, or the groin. The tendency of these areas to sweat and rub together makes for extra discomfort. In addition, they're more vulnerable to fungal infection.
In erythrodermic psoriasis, there are no individual lesions – the whole affected area is red and inflamed. In severe cases, the whole body can be covered.
In pustular psoriasis, the white blood cells rise to the surface to fill pustules. It is often found on the hands and the soles of the feet.
Sometimes psoriasis affects the nails. These can become brittle and cracked, or they may even separate from their beds.
These types of psoriasis aren't separate diseases – they are different symptoms of the same disease. In some cases, one person will have more than one type of psoriasis.
The most common complications of psoriasis are psychological – it affects a person's self-esteem, sociability, and quality of life. At worst, people can cut themselves off completely from the outside world. Fortunately, psoriasis lesions don't leave permanent scars on the skin, although the lesions may recur.
Psoriatic arthritis is a serious complication of psoriasis. This immune disease affects up to 30% of all psoriasis sufferers. Essentially, the same immune activity that affects the skin also attacks the joints. The disease is just as debilitating as rheumatoid arthritis, and affects the same joints: hands, feet, knees, hips, and spine.