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:
- alcohol consumption
- allergic reactions to medications
- chicken pox
- cold weather
- diseases that reduce the effectiveness of the immune system (e.g., HIV)
- hormonal changes
- infection from bacteria or viruses: a certain kind of lesion often appears for people with psoriasis after they've had a cold or a bacterial throat infection.
- medications (e.g., antimalarials, beta-blockers, and some anti-inflammatories)
- overusing or suddenly stopping the use of corticosteroid medications (often used to treat psoriasis)
- physical trauma or skin injury
- psychological stress
- severe sunburn
Symptoms and Complications
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.
Making the Diagnosis
There is no laboratory test for psoriasis. Most likely, your doctor will easily recognize this common disease from the type and location of the inflammation. There are, however, many diseases that can be confused with psoriasis: seborrheic dermatitis, eczema, lupus, syphilis, and some types of skin cancer, to name a few. Your doctor will need to perform a physical examination to eliminate these possibilities. Rarely, a skin biopsy (removing a small piece of skin and examining it) is needed to rule out other conditions that can cause similar symptoms to psoriasis.
Treatment and Prevention
A wide range of treatments are available to manage the flare-ups associated with all types and degrees of psoriasis. The goal of treatment is to prevent the formation of new lesions by modifying the body's immune mechanisms. Some treatments are "remittive" and some are "suppressive." Relief of symptoms that continues after the treatment is stopped is called a remission. It means that people with psoriasis may take a break from medication treatment. With other types of psoriasis treatments, the symptoms can return once the medication is stopped. When a medication is used continuously to keep symptoms at bay, this is known as suppression.
Moisturizers are vital for psoriasis. They won't clear it up, but they'll reduce the pain and itching, and may prevent flare-ups. It is also important to drink plenty of water.
There are dozens of creams and lotions people can apply. Coal tar has been used to great effect for centuries. It probably makes the skin more sensitive to UV light, and the two are often prescribed together. Coal tar is available without a prescription.
Topical (applied on the skin) medications that your doctor may recommend include salicylic acid*, anthralin, vitamin A-like agents (or retinoids; e.g., tazarotene), vitamin D-like agents (e.g., calcipotriol, calcitriol), and corticosteroids.
If topical treatments are not effective or if you have more severe psoriasis, oral medications (e.g., acitretin, cyclosporine, methotrexate) can be used for psoriasis treatment. These medications are taken by mouth and absorbed into the body. They work by affecting the body's immune system, which is overactive if you have psoriasis.
Another group of medications called biologics is used to treat moderate-to-severe psoriasis. Biologics are medications given by injection that work by targeting the immune system. Adalimumab, alefacept, etanercept, infliximab, and ustekinumab are examples of biologics used to treat psoriasis.
Sunlight (or phototherapy) can help people with certain skin disorders, including psoriasis. Keep in mind that prolonged exposure to the sun can increase the risk of sunburn, skin cancers, and cataracts. Remember to go easy – sunburn can cause a flare-up at the burn site. It is important to speak to your doctor before trying any light therapy. Always follow the directions provided by your health care provider when you are using light therapy treatment.
Light therapy includes UVB treatment, PUVA, and lasers. UVB treatment uses ultraviolet B light to treat the affected area. PUVA (psoralen plus ultraviolet A light) uses ultraviolet A light in combination with medication to make the skin more sensitive to the light. Laser treatment shines a focused beam of UVB light on the psoriasis plaques. All these phototherapies have side effects, so talk to your doctor about any questions you have if you are considering phototherapy for psoriasis.
For all treatments, it’s important to follow the directions for use and treatment schedule for your medication.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.