People who get psoriasis usually have one or more person in their family who has psoriasis. Not everyone who has a family member with psoriasis will get psoriasis.

What causes psoriasis?

Psoriasis is not contagious.You cannot get psoriasis from touching someone who has psoriasis.You cannot get psoriasis from swimming in the same pool or having sex.
Scientists have learned that a person’s immune system and genes play important roles. It seems that many genes must interact to cause psoriasis.
Scientists also know that not everyone who inherits the genes for psoriasis will get psoriasis. It seems that a person must inherit the “right” mix of genes. Then the person must be exposed to a trigger.

Many people say that their psoriasis began after they experienced one of these common psoriasis triggers:

A stressful event
Strep throat
Taking certain medicines, such as lithium or medicine to prevent malaria
Cold, dry weather
A cut, scratch or bad sunburn

Plaque psoriasis

Raised reddish patches on the skin called plaque (plak)
Patches may be covered with a silvery-white coating, which dermatologists call scale
Patches can appear anywhere on the skin
Most patches appear on the knees, elbows, lower back, and scalp
Patches can itch
Scratching the itchy patches often causes the patches to thicken
Patches vary in size and can appear as separate patches or join together to cover a large area
Nail problems — pits in the nails, crumbling nail, nail falls off

Guttate psoriasis

Small, red spots (usually on the trunk, arms, and legs but can appear on the scalp, face, and ears).
Spots can show up all over the skin.
Spots often appear after an illness, especially strep throat.
Spots may clear up in a few weeks or months without treatment.
Spots may appear where the person had plaque psoriasis.

Pustular psoriasis

Skin red, swollen, and dotted with pus-filled bumps.
Bumps usually appear only on the palms and soles.
Soreness and pain where the bumps appear.
Pus-filled bumps will dry, and leave behind brown dots and/or scale on the skin.

When pus-filled bumps cover the body, the person also may have:

Bright-red skin
Been feeling sick and exhausted
Severe itching
Rapid pulse
Loss of appetite
Muscle weakness

Inverse psoriasis

Smooth red patches of skin that look raw.
Patches only develop where skin touches skin, such as the armpits, around the groin, genitals, and buttocks. Women can develop a red, raw patch under their breasts.
Skin feels very sore where inverse psoriasis appears.

Erythrodermic psoriasis

Skin looks like it is burned.
Most (or all) of the skin on the body turns bright red.
Body cannot maintain its normal temperature of 98.6° F. Person gets very hot or very cold.
Heart beats too fast
Intense itching
Intense pain

If it looks like a person has erythrodermic psoriasis, get the person to a hospital right away. The person’s life may be in danger.