Psoriatic arthritis (PsA) is an inflammatory form of arthritis that causes swollen, stiff, and painful joints.

PsA affects about 30 percent of people with psoriasis, a skin condition characterized by scaly, red skin patches.

Hypothyroidism affects your thyroid — the butterfly-shaped gland in your neck that produces hormones. When you have hypothyroidism, this gland doesn’t make enough thyroid hormones.

The most common cause of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune condition in which white blood cells of the immune system mistakenly attack cells in the thyroid gland.

PsA and psoriasis are also autoimmune disorders. These conditions cause your immune system to attack healthy joints and skin. In hypothyroidism, your immune system’s target is the thyroid gland.

Read on to learn how these two conditions are related.

Psoriasis isn’t a symptom of hypothyroidism. But if you have psoriasis or PsA, you’re more likely to have at least one other autoimmune disease, including:

  • rheumatoid arthritis
  • Crohn’s disease
  • ulcerative colitis
  • hypothyroidism

In autoimmune thyroid disease, the immune system makes proteins called antibodies that damage the thyroid gland.

People with PsA and psoriasis are more likely to test positive for thyroid antibodies than people without these conditions. In one study, about a third of people with psoriasis had a thyroid condition, too.

Thyroid hormones act on many different parts of your body, including your skin. These hormones may trigger psoriasis and make symptoms worse.

Thyroid hormones increase the level of growth factors that cause the skin cells that form scaly psoriasis plaques to multiply. Excess thyroid hormone production makes psoriasis worse.

Hypothyroidism isn’t a skin disease. But like psoriasis and PsA, it can affect your skin.

Skin symptoms of hypothyroidism include:

  • dry, scaly skin that cracks
  • swelling of your hands, face, and eyelids, which are symptom of severe hypothyroidism, called myxedema
  • pale or yellow skin

A few different triggers can result in flares of psoriasis or make the skin condition worse. Common psoriasis triggers include:

  • stress
  • injury to the skin
  • infections such as strep throat or bronchitis
  • cold weather

Some medications also cause psoriasis flare-ups. Certain prescription drugs can:

  • worsen the plaques you already have
  • prevent your plaques from going away
  • trigger new psoriasis plaques

The medications most likely to cause a psoriasis flare-up are:

  • beta-blockers that treat heart disease
  • antimalaria drugs such as chloroquine
  • cancer drugs such as interferon and imiquimod
  • monoclonal antibodies, which treat cancer
  • the antifungal drug, terbinafine
  • lithium for bipolar disorder

It usually takes 2 to 3 weeks after you start taking a new drug for psoriasis symptoms to appear. If you stop taking a corticosteroid drug such as prednisone too quickly, it can also set off a psoriasis flare.

If you take one of these medications and notice that your psoriasis is getting worse, don’t stop taking it. Talk with your doctor instead. Ask if you can switch to another drug that won’t affect your skin.

Generalized myxedema is a complication of severe hypothyroidism. It causes:

  • waxy, doughy-looking skin
  • swelling of the lips, eyelids, and tongue
  • dryness

Doctors treat myxedema rash with corticosteroid creams and injections.

Pretibial myxedema (PTM) is a red, swollen, and thick skin rash. It’s a rare symptom of thyroid conditions such as Hashimoto’s thyroiditis and Graves’ disease.

This rash forms when hyaluronic acid, a natural lubricant your body makes, builds up under your skin. The affected skin becomes thick and has the texture of an orange peel.

PTM most often appears on the shins or the tops of the feet. It also can form on areas like your:

  • knees
  • shoulders
  • elbows
  • upper back
  • ears
  • nose
  • neck

Reach out to a doctor if you have symptoms of PsA or Hashimoto’s thyroiditis that don’t go away.

PsA symptoms include:

  • painful, swollen fingers and toes
  • stiffness, swelling, and pain in one or more joints
  • reduced range of motion in your joints
  • nail changes, such as a nail that has pits or separates from the nail bed
  • red, scaly patches of skin
  • itchy or burning skin
  • low back pain

Hashimoto’s thyroiditis symptoms include:

  • swelling in your neck, called a goiter
  • unusual tiredness
  • weight gain
  • muscle weakness
  • increased sensitivity to cold
  • dry skin and hair
  • brittle, splitting nails

Your doctor will ask about your symptoms and medical history. You may need blood tests to find out whether your thyroid hormone level is too low or imaging tests to check your joints for damage.

PsA and hypothyroidism are both types of autoimmune disorders. When you have PsA or psoriasis, you’re also more likely to have thyroid disease.

If you have symptoms of PsA or hypothyroidism, contact your doctor for an exam. Treatments can slow the joint damage and skin plaques of PsA as well as restore normal hormone levels in hypothyroidism.