What is autoimmune disease?

Written by Dr. Simon Khela MBChB MRCGP, GMC Registered Doctor

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I regularly see patients who describe a cluster of symptoms that don't quite add up. They may have persistent fatigue, aching joints with no obvious cause, or unpredictable skin flare-ups. Sometimes they simply feel that something is wrong, despite looking well. One of the most common concerns I see in practice is a patient asking, "Could this be autoimmune?" They may have spent weeks feeling dismissed or being told it is "just stress."

It's a fair question, and an increasingly common one. This article explains what autoimmune disease actually means, what the most common autoimmune disease symptoms look like, and how conditions such as rheumatoid arthritis, a familiar example, are diagnosed and managed in the UK.

A patient in her early thirties whom I saw a while ago had spent the best part of two years being treated for "stress" and mild anaemia before further assessment found thyroid autoantibodies and other findings consistent with Hashimoto's thyroiditis. Her story isn't unusual. It's one of the more common patterns I see with autoimmune disease generally: vague, fluctuating symptoms that get attributed to lifestyle or mental health long before anyone thinks to test for an underlying immune cause.

Quick Answer: What Is Autoimmune Disease?

Autoimmune disease is an umbrella term for more than 80 different conditions in which the immune system mistakenly attacks the body's own healthy tissue instead of just fighting infection. Depending on which tissues are targeted, this can affect a single organ, as in autoimmune thyroid disease, or several systems throughout the body, as seen in rheumatoid arthritis or lupus.

How Does the Immune System Normally Work?

Before explaining what goes wrong in autoimmune disease, it helps to understand what your immune system is meant to do. In simple terms:

• It identifies bacteria, viruses, and damaged cells, then responds to them
• It's able to distinguish between "foreign" material and your own healthy tissue
• Once a threat has passed, the immune response is meant to stand down

Many patients are surprised to learn that autoimmune disease is not simply a sign of a "weak" immune system. It involves an immune response directed at the body's own tissues. For more background, see our guide to how the immune system works.

What Is Autoimmune Disease, Exactly?

In autoimmune disease, the immune system loses the ability to reliably tell the difference between "self" and "non-self." Immune cells and, in some conditions, antibodies called autoantibodies react against the body's own tissues. This can cause inflammation and, depending on the condition, tissue damage. An autoantibody result alone does not establish a diagnosis.
A few things worth understanding early on:

• There is no single "autoimmune disease". The term describes dozens of distinct conditions, each with its own target tissue, symptoms and treatment
• Most are chronic, meaning they're managed rather than cured, typically with periods of flare and periods of relative calm
• They can overlap. It's entirely possible to have more than one autoimmune condition at once, which is one reason diagnosis can take time

How Common Is Autoimmune Disease in the UK?

Autoimmune disease is far more common than most people assume. A large 2023 study of 22 million UK health records, led by researchers at Oxford University and UCL, found that these conditions affect around 10% of the population. The study estimated a prevalence of roughly 13% in women and 7% in men, higher than some earlier estimates. The figure depends on which conditions are included and how cases are counted. This kind of large-scale data matters because individually, many autoimmune conditions are rare, which historically made overall prevalence difficult to pin down.

Organ-Specific vs Systemic Autoimmune Disease

One distinction I find useful when explaining this to patients is whether a condition is organ-specific or systemic.

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Common Types of Autoimmune Disease

Rheumatoid Arthritis: The Most Widely Recognised Example

Rheumatoid arthritis (RA) is probably the autoimmune condition most people have heard of, and it's a useful illustration of how these diseases behave. In RA, the immune system attacks the synovium, which lines the joints. This causes pain, swelling and stiffness that's typically symmetrical and worse first thing in the morning.
A question I am frequently asked is whether joint pain automatically means RA. It does not. Persistent joint swelling and morning stiffness warrant assessment; NICE guidance advises urgent referral for suspected persistent synovitis, even when inflammatory blood markers or antibody tests are normal. See our rheumatoid arthritis guide for a closer look at its symptoms and treatment.

Other Common Autoimmune Conditions

Beyond RA, some of the autoimmune diseases I see most often in clinic include:

• Lupus (systemic lupus erythematosus): a systemic condition that can affect joints, skin, kidneys and other organs, often causing a distinctive facial rash and disproportionately affecting women of childbearing age
• Type 1 diabetes: the immune system destroys insulin-producing cells in the pancreas, usually presenting with thirst, frequent urination and weight loss, as NHS information on the condition sets out in more detail; diabetes testing can help confirm a diagnosis when these symptoms appear, and Diabetes UK is a well-established source of ongoing patient support
• Coeliac disease: the immune system reacts to gluten, damaging the lining of the small intestine and, according to the NHS, affecting roughly 1 in 100 people in the UK; we've covered coeliac disease in more detail separately
• Autoimmune thyroid disease: includes Hashimoto's thyroiditis (underactive thyroid, causing fatigue and weight gain) and Graves' disease (overactive thyroid, causing weight loss and a racing heart)
• Psoriasis and psoriatic arthritis: affect the skin and sometimes the joints, with flares often triggered by stress or infection
• Multiple sclerosis (MS): affects the brain and spinal cord, with symptoms ranging from visual disturbance to problems with coordination
• Vitiligo: affects pigment-producing skin cells, causing patches of skin to lose their colour

Autoimmune Disease Symptoms

Individual autoimmune conditions have their own specific features, but there's also a set of overlapping symptoms that many share, which is precisely why these conditions are so easy to miss early on:

• Persistent fatigue that doesn't improve with rest
• Joint or muscle pain and stiffness
• Low-grade fevers
• Skin changes, including rashes, dryness or unusual pigmentation
• Hair thinning or loss
• Digestive symptoms such as bloating or altered bowel habits
• "Brain fog", such as difficulty concentrating or finding words
• Swollen glands

Can an Autoimmune Disease Cause a Skin Rash?

Yes, some can, but a rash alone does not mean you have an autoimmune disease. Lupus may cause a rash across the cheeks and nose or a rash made worse by sunlight; psoriasis causes scaly plaques, and vitiligo causes patches of lost skin colour. Their appearance and treatment differ, and many common rashes have non-autoimmune causes. Photograph a rash when it flares and note any joint symptoms, fevers or other changes to discuss with a clinician. A rapidly spreading rash with breathing difficulty, facial swelling or severe illness needs urgent medical attention.

Why Autoimmune Symptoms Are Easy to Miss

Many patients are surprised to learn just how long it can take to reach an autoimmune diagnosis, sometimes years. A few reasons for this come up repeatedly in my clinical experience:

• Early symptoms overlap heavily with common, less serious causes of fatigue, such as poor sleep or stress
• Symptoms often fluctuate, so they can seem to resolve before a pattern becomes clear
• Many autoimmune conditions have no single definitive test. Diagnosis relies on a combination of clinical picture, blood results and, sometimes, imaging or biopsy
• Some people test negative on standard antibody panels despite having a genuine autoimmune condition

Can You Prevent Autoimmune Disease?

There is no proven way to prevent every autoimmune disease. Genetics and factors outside your control play a role, so a diagnosis is not evidence that you caused it. Avoiding smoking and looking after general health are sensible steps, and some condition-specific risks may be reduced, but supplements, special diets and “immune-boosting” products have not been shown to prevent autoimmune diseases as a group. Speak to a clinician if you have a strong family history or persistent symptoms rather than paying for broad screening panels without a clear clinical question.

What Causes Autoimmune Disease?

As with rheumatoid arthritis specifically, the honest answer for autoimmune disease as a whole is that we don't fully understand what triggers it. What we do know points to an interaction between genetics and environment.

• Genetics. Certain genes, particularly within the HLA (human leukocyte antigen) system, are linked to increased risk across multiple autoimmune conditions. Having a family member with one autoimmune disease modestly raises the risk of developing another, even a different one.
• Sex and hormones. Women are affected more often than men for many autoimmune diseases. The difference varies by condition and can be particularly marked in lupus. The reasons aren't fully settled, but hormonal and genetic factors are both thought to play a part.
• Environmental triggers. Infections, smoking, and certain medications have all been linked to triggering autoimmune activity in genetically susceptible people.
• Gut health. There's growing research interest in the role of the gut microbiome in regulating immune function, though this remains an evolving area.
• Vitamin D status. Reduced vitamin D levels have been associated with several autoimmune conditions, although whether low vitamin D is a cause or simply a consequence of chronic inflammation is still debated.
• Stress. While stress doesn't cause autoimmune disease on its own, many patients report that flares coincide with particularly stressful periods, and this pattern is increasingly recognised in research too.

How Are Autoimmune Diseases Diagnosed?

Diagnosis usually follows a similar pattern regardless of which condition is suspected:

1. A detailed history and examination, looking for patterns in the affected joints or organs and how symptoms have changed over time
2. Targeted blood tests, when the history and examination suggest a particular condition. Blood tests may include ANA for suspected systemic connective-tissue disease, rheumatoid factor and anti-CCP for RA, thyroid antibodies or tissue transglutaminase antibodies for coeliac disease. An ANA result is not a general yes-or-no test for all autoimmune diseases
3. Inflammatory markers, such as CRP and ESR, which may support the clinical picture but can be normal in some conditions
4. Imaging or biopsy, where relevant. Examples include imaging for suspected joint damage in RA or, in some cases, a gut biopsy to confirm coeliac disease
5. Specialist referral. Depending on which organ system is affected, this might mean a rheumatologist, endocrinologist, gastroenterologist, dermatologist or neurologist. Getting a referral to the right specialist promptly matters, since several autoimmune conditions respond better to treatment started early

A question I am frequently asked is whether a negative blood test rules out autoimmune disease. Not necessarily. Some patients are "seronegative" on standard panels yet still have a genuine autoimmune condition based on their clinical picture, and diagnosis sometimes needs to be revisited over time as the disease evolves.

How Is Autoimmune Disease Treated?

Treatment varies enormously depending on which condition and which organs are involved, but some broad principles apply across most autoimmune diseases:

• Suppressing or modulating the immune response: medicines may range from short-term steroids to long-term disease-modifying drugs and biologics, as used in RA
• Replacing what's lost. In type 1 diabetes, this means insulin; in autoimmune thyroid disease, thyroid hormone replacement
• Removing the trigger where possible. In coeliac disease, a strict lifelong gluten-free diet is the primary treatment
• Symptom control: pain relief, skin treatments or physiotherapy may be used alongside disease-specific treatment, depending on what is affected
• Regular monitoring, since most autoimmune conditions need periodic blood tests and specialist review to track disease activity and treatment safety over time

There's no single "cure" for autoimmune disease as a category, and I think it's important to be upfront about that rather than overstate what treatment can achieve. However, some autoimmune conditions, including RA, can reach remission or low disease activity with appropriate treatment. Outcomes vary by condition and person.

Living With an Autoimmune Disease

Day-to-day management goes well beyond medication. A few things I discuss regularly with patients:

• Pacing fatigue. Chronic fatigue from autoimmune disease doesn't always respond to rest the way ordinary tiredness does, and learning to pace activity is often more helpful than pushing through or resting completely
• Mental health. Living with an unpredictable, chronic condition takes a genuine toll, and low mood or anxiety are common, legitimate parts of the picture rather than something to push aside; support for depression and anxiety is a reasonable thing to ask for alongside physical treatment
• Flare planning. Most autoimmune conditions fluctuate, and having a plan that explains who to contact and what to adjust during a flare reduces a lot of the anxiety around unpredictability
• Coordinated care. Where more than one autoimmune condition or specialist is involved, keeping your GP in the loop as the central point of contact helps prevent things falling between gaps
• Family planning. Some autoimmune medications aren't safe in pregnancy, and certain conditions, including lupus, need specialist input well before conception, so it's worth raising this early if it's relevant to you

Common Myths and Misconceptions About Autoimmune Disease

"It's basically the same as having allergies."

Allergies involve the immune system overreacting to something harmless from outside the body. Autoimmune disease involves the immune system attacking the body's own tissue. These are different mechanisms.
"Only older people get autoimmune diseases."

Many autoimmune conditions, including lupus and type 1 diabetes, commonly present in children, teenagers, and young adults. Others, like RA, most often appear in mid-life but can occur at any age.
"If your blood tests are normal, you don't have an autoimmune disease."

As above, some genuine autoimmune conditions present with normal or borderline results on standard testing, particularly early on.
"Diet alone can cure autoimmune disease."

Diet can play a supportive role. A strict gluten-free diet is the treatment for coeliac disease, but for most autoimmune conditions, no diet has been proven to replace medical treatment.
"All autoimmune diseases are essentially the same condition."

They share a broad mechanism, but they behave very differently depending on which tissues are affected, which is why treatment is tailored to the specific diagnosis rather than applied generically.

When Should You See a GP?

I'd generally encourage anyone to seek an assessment if they notice:

• Persistent fatigue that doesn't improve with adequate rest
• Joint pain, swelling or stiffness lasting more than a few weeks
• Unexplained skin changes, rashes or hair loss
• Recurrent low-grade fevers without an obvious cause
• A family history of autoimmune disease alongside new, persistent symptoms

If getting a timely appointment is proving difficult, you can book an online GP consultation as a starting point for assessment and, where appropriate, onward referral.

Frequently Asked Questions