What Are Plaques And Why Do They Form?

Reviewed by: HU Medical Review Board | Last reviewed: July 2016.

What are plaques?

Plaque psoriasis is a chronic skin condition that affects the lives of millions of people worldwide. Psoriasis causes a person’s skin to develop a series of small red or pink bumps, which can grow in size and become covered in silvery white scales.1 The skin can then become more and more inflamed and thickened, until the affected patches of skin form what are called plaques.

What causes plaques to form?

People develop psoriasis plaques because their overactive immune system causes their body to create new skin cells too quickly. In people without psoriasis, the body usually produces new skin cells every month or so. These new skin cells move to the surface of the skin and replace the old skin cells that are shed naturally from the body. In people with psoriasis, the body produces these new skin cells far too quickly - about every 3 or 4 days, instead of every month.1 Because the new skin cells are created so quickly, the body does not have enough time to shed older skin cells. The new cells push the older cells too quickly to the top surface of the skin, where the cells build up and cause psoriasis plaques.

Why do psoriasis plaques form in some people, but not in other people?

While scientists do know how plaques are formed, they are still working to understand exactly why some people’s bodies produce skin cells too quickly. Research has shown that there does seem to be a genetic link to psoriasis. This means that the members of certain families have a greater chance of developing psoriasis than the members of other families2 But not all of the members of these families actually develop the disease, so scientists still do not know exactly what makes some people’s bodies produce too many skin cells.

Research has also found that people with plaque psoriasis generally have certain triggers that cause them to develop the condition for the first time, or cause flare-ups of the disease (when symptoms get worse for a period of time). While scientists know that these triggers do exist, they still do not know precisely how they work in different people. Common triggers for people with plaque psoriasis are skin injury, infections, stress, and taking certain kinds of medications.4

How is the immune system linked to plaque psoriasis?

What scientists do agree about is that the body’s immune system plays a key part in causing plaque psoriasis. Specifically, they think that psoriasis in all of its forms is an “autoimmune” disease.

The function of the immune system is to fight off substances in the body than can cause illnesses, which are called “antigens.” Bacteria and viruses are examples of antigens. Special types of white blood cells called “T cells” are an important part of the immune system’s protective response. They travel all around the body in the bloodstream, searching for and attacking antigens.3

The immune system does not function quite like it is supposed to in people with plaque psoriasis. Instead of attacking antigens, the immune system starts to attack a person’s own healthy body tissues. This is called “autoimmunity.” One of the main weapons that the immune system uses to attack is the process of inflammation.4

How is inflammation involved in plaque psoriasis?

T-cells attack antigens by triggering the body’s natural process of inflammation. In people with plaque psoriasis, the T-cells trigger inflammation to attack healthy tissues in the body by mistake.

Inflammation causes the blood vessels in certain parts of a person’s body to become larger, which allows other types of white blood cells to pass through. In a person with plaque psoriasis, this inflammation happens in the skin. As a result of the inflammation, the body keeps producing a large amount of healthy new skin cells, as well as the new T-cells and other white blood cells. This process is what begins the cycle of producing too many new skin cells, which go on to cause psoriasis plaques.3

Scientists know that this process of inflammation is what causes plaques to form on the skin, but they are still searching to find out how and why a person’s immune system can be tricked into attacking healthy body tissues. While there is still much work to be done, this area of research has led to the development of new and powerful drugs for treating people with plaque psoriasis. These drugs work by changing the way that the immune system functions in order to change this inflammatory process and stop it from attacking healthy tissues.4 For people with severe plaque psoriasis, these new drugs are a huge breakthrough in controlling their symptoms and improving their quality of life.

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