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Moderate to severe psoriasis describes how much of your body is covered in red, scaly psoriasis patches.

  • Moderate psoriasis covers 3% to 10% of your body.
  • Severe psoriasis covers more than 10% of your body.

Knowing that you have moderate or severe psoriasis helps your doctor decide on a treatment. However, it's not the only factor involved in choosing a treatment.

You may have moderate psoriasis that really bothers you and want to start on a strong treatment. Or you may have more severe psoriasis that you barely notice and want to start with a milder treatment.

Your doctor will also consider these factors when helping you choose a treatment:

  • The type of psoriasis you have
  • How much psoriasis affects your life
  • Your health

Your doctor may use the Koo-Menter Psoriasis Instrument to help decide which treatment you need. This one-page tool asks questions to find out how much psoriasis is affecting your life.

Usually, doctors start with the mildest treatments. If the first treatment doesn't work, you'll move up to stronger and stronger treatments until you find one that clears your psoriasis.

If you have very severe psoriasis, you may need to take more than one of these drugs at a time. Sometimes adding ultraviolet light or sunlight to a psoriasis pill, injection, or cream can help it work better.

Treatments for Moderate to Severe Psoriasis

Even though everyone with psoriasis is different, doctors have a few standard treatments that they try in people with moderate to severe psoriasis. These include:

  • Light therapy (phototherapy)
  • Medications that suppress your immune system or target specific immune responses linked to psoriasis.

These treatments aim to slow down the rapid skin cell growth in psoriasis. They can also help smooth out scaly skin and reduce inflammation.

Light Therapy (Phototherapy)

Your dermatologist may have told you to stay out of the sun to prevent skin cancer and aging. But in people with psoriasis, the sun's ultraviolet A and B (UVA and UVB) rays can actually help clear the skin.

Some doctors recommend sitting outside in the sun for a few minutes a day. Or you can try an indoor light therapy that simulates UVA or UVB rays.

Here are three types of light therapy for psoriasis. 

1. Ultraviolet B (UVB) Therapy

What it is: Ultraviolet B (UVB) therapy uses the same type of ultraviolet radiation found in sunlight. It's used to treat psoriasis that doesn't respond to creams and lotions.

How it works: Your body is exposed to UVB light from a light box in a doctor's office or at home. The UVB light goes into your skin and slows skin cell growth.

Types of UVB therapy:

  • Broadband UVB therapy -- releases a wide band of ultraviolet light
  • Narrow-band UVB therapy -- releases a narrow band of ultraviolet light to target small areas of the skin
  • Goeckerman therapy -- you apply coal tar to the skin before being exposed to UVB light

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