Arthus Reaction
Informed by recognized medical guidance
Overview
An Arthus reaction is a localised (in one area) immune system response that can happen after a vaccination or an injection. It causes pain, swelling, redness, and hardening at the injection site, usually starting a few hours after the shot. It is not a true allergic reaction to the vaccine, but rather a response caused by immune complexes — clumps of antibodies and the injected substance — forming in the small blood vessels under the skin.
Key facts
- It usually appears 4 to 12 hours after an injection.
- It is a considered a type III hypersensitivity reaction, meaning it involves immune complexes in the body.
- It typically resolves on its own within a few days without long-term harm.
Arthus reaction is uncommon. Most people who receive vaccinations or injections do not develop this reaction.
Arthus reactions can affect anyone who receives certain vaccines or injected medications. They are very rare, but they have been reported more often after booster doses of vaccines such as tetanus and diphtheria.
Symptoms
- Trouble breathing or shortness of breath
- Swelling of the lips, tongue, face, or throat
- Feeling dizzy, faint, or collapsing
- A widespread rash or hives that appear rapidly after the injection
- ⚠Swelling that keeps getting bigger after 24 hours
- ⚠High fever or chills
- ⚠Signs of infection such as red streaks, increasing heat, or pus
- ⚠Severe pain that stops you from moving the injected arm or leg
Common symptoms
- Pain, tenderness, or discomfort at the injection site
- Redness and swelling around the area where the injection was given
- A firm, hard lump (induration) under the skin at the injection site
- Warmth and itching around the injection site
- Mild general discomfort or a low-grade feeling of being unwell
Symptoms in children
- Children may cry, complain of pain, or favour the arm or leg that was injected
- The injection site may look red, swollen, and feel warm
- A child may be fussy or less hungry than usual for a day
Symptoms in older adults
- Swelling and redness may be more noticeable or last slightly longer in older adults
- The reaction might be mistaken for a skin infection, so it is important to have it checked if it worsens
- Fragile skin may make bruising or soreness more obvious
Causes
Main causes
- Repeated exposure to the same vaccine or injected substance can trigger an Arthus reaction
- It happens when antibodies and the injected substance form clumps called immune complexes in the blood vessels of the skin
- It can occur after certain vaccines, such as tetanus or diphtheria boosters, or after receiving certain injected treatments
Risk factors
- Having high levels of antibodies already in your blood from a recent vaccination or infection
- Receiving booster injections frequently or in the same muscle area over time
- A personal history of hypersensitivity reactions to vaccines or injectable medications
When to see a doctor
See a doctor urgently if:
- Seek same-day medical advice if the swelling and redness are getting worse, not better, after 24 hours
- See a doctor promptly if you develop a high fever, chills, or signs of infection
- Contact your GP or local health service if the pain is severe and does not ease with simple measures
Book a routine appointment if:
- Tell your doctor or practice nurse about any previous injection reactions during your next routine appointment
- If you are due a future vaccine, discuss your Arthus reaction with your healthcare provider so they can plan the safest approach
Diagnosis
A doctor usually diagnoses an Arthus reaction by examining the injection site and asking about when you had the injection and how the reaction has changed over time. The timing and characteristics are often enough to tell it apart from an infection or a true allergy.
Tests that may be done
- No specific test is usually needed
- Your doctor may gently press the area to check for a firm lump
- In rare or unclear cases, a small skin sample (biopsy) or blood tests might be arranged
What to expect at your appointment
During your appointment, the doctor or nurse will ask about your symptoms and medical history, examine the injection site, and explain what is happening. They can reassure you about what to expect and whether you need any treatment.
Treatment
Treatment for an Arthus reaction focuses on relieving symptoms while the body's immune system settles down. In most cases, the reaction fades on its own within a few days.
Self-care at home
- Apply a clean, cool, damp cloth to the injection site to help reduce swelling and pain
- Rest the limb that received the injection for the first day
- Take simple measures to keep the area clean and dry
- Ask your pharmacist or doctor about suitable over-the-counter pain relief
Medical treatments
If the reaction is severe, a doctor may recommend an anti-inflammatory medicine or another treatment to reduce inflammation and discomfort. These are only used under close medical supervision. In rare cases, your doctor may discuss adjusting your future vaccination schedule to avoid another reaction.
When is surgery considered?
Surgery is not used to treat an Arthus reaction.
Living with this condition
Most people recover fully within 1 to 3 days. You can return to normal daily activities as soon as you feel comfortable, but avoid strenuous exercise or heavy lifting using the injected limb until the swelling goes down.
Lifestyle tips
- Keep the injection site cool with a gentle cloth or cold pack if it feels sore
- Drink plenty of fluids to stay well hydrated
- Rest the affected arm or leg during the first 24 hours
- Watch the area for any concerning changes, such as worsening redness or discharge
Diet and exercise
A normal balanced diet is fine. Gentle movement is okay, but avoid intense workouts or heavy lifting of the injected limb until the inflammation settles. Listen to your body and stop if you feel pain.
Mental health and emotional wellbeing
Having a reaction after a vaccine can be worrying, especially if you were not expecting it. Remember that an Arthus reaction is usually temporary and does not mean your overall health is at risk. If you feel anxious about future injections, talk to your healthcare provider—they can offer support and make a plan to keep you comfortable.
Prevention
An Arthus reaction cannot always be prevented, but telling your doctor or nurse about any previous injection reactions can help them take precautions. For example, they may decide to give a vaccine in a different part of the body or wait longer between doses.
Vaccines
If you are due a booster vaccine and have had a moderate or severe Arthus reaction in the past, your doctor may wait a few months before giving it, or use a different vaccine brand if appropriate. Always discuss your vaccination history with your healthcare provider first.
Complications
If left untreated
- Usually there are no long-term complications, even without treatment
- Rarely, severe swelling can cause temporary stiffness or reduced use of the affected limb
- In very rare cases, a severe reaction can lead to skin breakdown or tissue damage, which would need medical attention
Long-term outlook
The outlook is excellent. An Arthus reaction almost always clears up completely on its own, usually within a few days. Having one does not mean you can never receive vaccines again—it simply means your healthcare team can tailor future vaccinations to reduce the chance of it happening again.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: August 2, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.