What Is Hashimoto’s Disease? A Nurse Explains the Basics

By Anna Curran, RN, BSN, PHN · Last reviewed October 2026

Hashimoto’s disease is an autoimmune condition where your immune system attacks your thyroid gland by mistake. Over time, that damage can leave the thyroid unable to make enough hormone, which is called hypothyroidism. It is the most common cause of an underactive thyroid in the United States, and it is very treatable.

If you just heard this diagnosis, or you suspect it, you probably have a lot of questions. So, what is Hashimoto’s disease, and what does it mean for your daily life? Let’s walk through it in plain language.

What Is Hashimoto’s Disease?

Your thyroid is a small, butterfly-shaped gland at the front of your neck. It makes hormones that help set the pace for your whole body. Thyroid hormone affects your energy, heart rate, body temperature, digestion, skin, hair and mood.

In Hashimoto’s disease, the immune system makes antibodies that target the thyroid. White blood cells build up in the gland and cause inflammation. Slowly, the thyroid gets damaged and makes less hormone.

You may hear other names for it. Doctors also call it Hashimoto’s thyroiditis, chronic lymphocytic thyroiditis or autoimmune thyroiditis. “Thyroiditis” simply means inflammation of the thyroid.

How Hashimoto’s Causes Hypothyroidism

Hashimoto’s usually moves very slowly. The American Thyroid Association notes it often progresses over many years. Some people have antibodies for a long time while their thyroid still works normally.

Here is the usual pattern:

The immune attack starts. Antibodies form, and the thyroid becomes inflamed. You may feel nothing at all.
The thyroid works harder. Your brain senses that hormone levels are slipping. The pituitary gland sends out more thyroid-stimulating hormone (TSH) to push the thyroid along.
Hormone levels fall. If enough of the gland is damaged, it can no longer keep up. That is hypothyroidism.

Not everyone reaches the last step. Some people with Hashimoto’s never need treatment and just get regular blood tests. For those who do develop hypothyroidism, it is often permanent.

What about goiter?

Inflammation can make the thyroid swell. A swollen thyroid is called a goiter. It can make the front of your neck look full and may cause a feeling of pressure in your throat. It is usually not painful.

According to NIDDK, after many years the gland may shrink and the goiter may go away.

Can it cause an overactive thyroid?

Rarely, yes. Early on, damaged cells may leak stored hormone into the blood. This can cause short-lived symptoms of an overactive thyroid, such as a fast heartbeat or feeling jittery. This is not common, and it usually does not last.

Who Gets Hashimoto’s Disease?

Anyone can get Hashimoto’s at any age, including children. But some groups are much more likely to have it.

Women. It is 4 to 10 times more common in women than in men, according to NIDDK and Cleveland Clinic.
Middle age. It most often shows up between ages 30 and 50.
Family history. It tends to run in families. Your risk goes up if a parent, sibling or other relative has thyroid disease.
Other autoimmune conditions. Having one autoimmune disease raises the chance of another. Conditions linked with Hashimoto’s include celiac disease, type 1 diabetes, lupus, rheumatoid arthritis, Sjögren’s syndrome, pernicious anemia and Addison’s disease.
Pregnancy. Mayo Clinic notes that normal immune changes during pregnancy may play a role in thyroid disease that starts after a baby is born.
Radiation exposure. High levels of environmental radiation are linked to a higher risk.

Researchers still do not know exactly what sets off the immune attack. It is likely a mix of genes and things in the environment. There is no known way to prevent it.

If you have Hashimoto’s, nothing you did caused it. You did not bring this on yourself.

What Are TPO Antibodies?

TPO stands for thyroid peroxidase. It is an enzyme your thyroid uses to make hormones. In Hashimoto’s, the immune system makes antibodies against it.

Most people with Hashimoto’s have TPO antibodies in their blood, according to NIDDK and Mayo Clinic. That is why this blood test is so helpful for diagnosis. Some people also have thyroglobulin antibodies, which target a different thyroid protein.

A few things are good to know about TPO antibodies:

A positive test does not always mean you need medicine. If your TSH and thyroid hormone levels are normal, the American Thyroid Association says you do not need thyroid hormone treatment. Your doctor will likely check your TSH over time instead.
Your doctor may not repeat the antibody test. The ATA says repeat antibody testing is not needed. TSH is the number that guides care.
Some people have antibodies but never get thyroid disease. Others go on to develop hypothyroidism later. Regular checkups help catch changes early.

Common Symptoms

Many people have no symptoms early on. When the thyroid slows down, symptoms tend to creep in slowly. They can include:

Tiredness and feeling sluggish
Feeling cold when others are comfortable
Constipation
Dry skin, brittle nails or thinning hair
Weight gain
Muscle aches and joint stiffness
Heavy or irregular periods
Low mood
Trouble with memory or focus
A puffy face or swelling in the neck

These symptoms overlap with many other health problems. That is why a blood test is the only way to know for sure. You can read more in our guide to Hashimoto’s symptoms and diagnosis.

How Hashimoto’s Is Treated

If your thyroid is still making enough hormone, you may not need treatment yet. Your doctor will watch your symptoms and check your blood levels.

If you have hypothyroidism, the standard treatment is levothyroxine. It is a man-made version of T4, the main hormone your thyroid makes. NIDDK notes it is identical to your body’s own T4. It comes as a pill, a liquid or a soft gel capsule.

Most people take it once a day, usually in the morning before eating. Your doctor will check your TSH about 6 to 8 weeks after you start or change your dose. Once your dose is right, checks usually spread out to every 6 months, then once a year.

Most people with hypothyroidism from Hashimoto’s need thyroid hormone for life. Never stop it or change your dose without talking to your doctor. Too much thyroid hormone can lead to problems like an irregular heartbeat or bone loss.

What Happens If It Is Not Treated?

Untreated hypothyroidism can affect your whole body over time. Possible problems include:

High cholesterol
Heart disease and heart failure
High blood pressure
Depression
Pregnancy problems, such as miscarriage or preterm birth
A large goiter that makes swallowing or breathing harder

Rarely, very severe, long-term hypothyroidism can lead to myxedema coma. This is a life-threatening emergency where the body’s functions slow down dangerously.

Call 911 or go to the ER right away if you or someone with hypothyroidism has trouble breathing, extreme sleepiness or confusion, a very low body temperature or a very slow heartbeat. Also get emergency care for a swollen neck that makes it hard to breathe or swallow.

What Is the Outlook?

The outlook for Hashimoto’s disease is very good. Cleveland Clinic describes it as excellent with lifelong monitoring and treatment. With the right dose of thyroid hormone, most people live full, active lives. With proper treatment, Hashimoto’s should not shorten your life.

It can take some time to find your best dose, and it is normal for your dose to change over the years. Keep your follow-up appointments, and tell your doctor if symptoms come back or change.

Hashimoto’s is a long-term condition, but it is also one of the most well-understood and manageable ones.

Frequently Asked Questions

Is Hashimoto’s disease the same as hypothyroidism?

Not exactly. Hashimoto’s is the autoimmune condition that damages the thyroid. Hypothyroidism is the low hormone level that can result. You can have Hashimoto’s for years before hypothyroidism develops, and some people never develop it.

Is Hashimoto’s disease serious?

It is a lifelong condition, but it is very treatable. Untreated hypothyroidism can cause heart and pregnancy problems, so regular checkups matter. With treatment and follow-up, most people do well.

Can Hashimoto’s be cured?

There is no cure that stops the immune attack. But the low thyroid hormone it causes can be replaced with daily medicine. When your levels are in a healthy range, symptoms usually improve.

Should my family get tested?

Hashimoto’s often runs in families. If you have a relative with thyroid disease and you notice symptoms, ask your doctor whether a thyroid blood test makes sense for you.

The Bottom Line

Hashimoto’s disease is an autoimmune condition in which the immune system slowly damages the thyroid. It is the most common cause of hypothyroidism in the United States and is much more common in women. Not everyone with TPO antibodies needs treatment, but everyone with Hashimoto’s benefits from regular TSH checks. When hypothyroidism develops, daily levothyroxine and steady follow-up help most people feel well and live normal lives.