Quick answer: Red flags are symptoms that need urgent medical help rather than self-care. For people with arthritis, they include a suddenly hot, red, swollen joint with fever, signs of infection on immune-suppressing medicines, back pain with numbness around the bottom or bladder changes, new headache or vision change over 50, and chest pain or breathlessness.
Most changes in arthritis symptoms are part of the condition: a flare, a bad night, stiffness after a busy day. But some symptoms are warning signs of something more serious that needs medical help quickly. Clinicians call these "red flags". Knowing them means you can manage everyday ups and downs with confidence, and act fast on the rare occasions when it matters. This guide lists the key red flags for people living with arthritis, what they might mean, and exactly who to contact.
If you think someone's life is at risk, call 999. If you are not sure how urgent something is, call NHS 111 or use 111 online. They can direct you to the right service.
Quick reference: red flags and who to call
| Red flag | Possible cause | What to do |
|---|---|---|
| One joint suddenly hot, red, swollen and very painful, especially with fever or feeling unwell | Joint infection (septic arthritis) | NHS 111 or A&E, urgently |
| Fever, chills, feeling very unwell, confusion or fast breathing, especially on immune-suppressing medicines | Serious infection or sepsis | 999 or A&E if very unwell; otherwise same-day GP, rheumatology or NHS 111 |
| Back pain with numbness around the genitals or anus, bladder or bowel changes, or weakness or numbness in both legs | Cauda equina syndrome | 999 or A&E immediately |
| Over 50 with new headache, scalp tenderness, jaw pain on chewing, or vision changes | Giant cell arteritis | Same-day urgent help; 999 or A&E for any vision loss |
| Chest pain, sudden breathlessness, coughing blood | Heart attack, blood clot in the lung | 999 |
| Calf pain, swelling and warmth in one leg | Deep vein thrombosis (DVT) | NHS 111 or urgent GP; 999 if breathless or chest pain |
| Face drooping, arm weakness, speech problems | Stroke | 999 |
| Unable to weight-bear or a joint looks misshapen after a fall | Fracture or dislocation | Urgent treatment centre or A&E |
| Unexplained weight loss, fevers, night sweats, or new bone pain with a history of cancer | Infection, cancer or other serious illness | See your GP soon |
| Black, tarry stools or vomiting blood, especially on anti-inflammatories or steroids | Stomach bleeding | 999 or A&E |
1. A hot, red, swollen joint with fever
Septic arthritis is an infection inside a joint. The NHS describes it as a medical emergency, because it can damage the joint quickly and cause serious illness. It usually affects one joint, often the knee or hip, which becomes suddenly very painful, swollen, hot and red, and hard to move. You may have a high temperature and feel unwell.
People with existing arthritis, joint replacements, diabetes or immune-suppressing medicines are at higher risk. It can look like a flare or gout, which is why a single hot joint with fever should never be assumed to be "just arthritis". Read more in our guide to septic arthritis.
What to do: call NHS 111 or go to A&E urgently. If you have a joint replacement and it suddenly becomes hot, swollen and painful, contact your surgical team or go to A&E.
2. Signs of infection on immune-suppressing medicines
Many arthritis treatments, including methotrexate, sulfasalazine, leflunomide, biologics, JAK inhibitors and steroid tablets, can lower your ability to fight infection. The NHS methotrexate side effects page advises telling your doctor or calling 111 immediately if you get signs of an infection, such as a high temperature, muscle aches or a sore throat.
Watch for:
- A high temperature, or feeling hot and shivery
- Sore throat, mouth ulcers or a new cough
- Pain when passing urine
- Red, hot, painful skin
- Feeling generally very unwell
Sepsis is a life-threatening reaction to an infection. The NHS lists common symptoms in adults including confusion or slurred speech, uncontrollable shivering, muscle pain, difficulty breathing, blue, pale, grey or blotchy skin, lips or tongue, a high or low temperature (a high temperature is less common in older adults), and not peeing all day or peeing very little. Call 999 or go to A&E if you or someone you care for may have sepsis.
What to do for other infection signs: contact your GP or rheumatology advice line the same day, or NHS 111 out of hours. Do not stop or pause arthritis medicines yourself unless your team has told you to, and never stop steroid tablets suddenly. If you take steroids, carry your steroid emergency card and show it to health professionals.
3. Back pain with nerve warning signs
Back pain is very common and usually not serious. But the NHS advises calling 999 or going to A&E if you have back pain with certain nerve warning signs, which can mean nerves at the bottom of the spine are being compressed (cauda equina syndrome). These include:
- Pain, tingling, weakness or numbness in both legs
- Loss of feeling around your genitals or anus
- Changes in your bladder or bowels, such as difficulty peeing, or peeing or pooing yourself
- Changes in sexual sensation or function
- Back pain that started after a serious accident, or back pain with chest pain
The NHS advises an urgent GP appointment or NHS 111 for back pain if you feel hot, cold, shivery or generally unwell, or if severe pain starts suddenly or gets worse quickly. Other back pain warning signs that need a prompt GP assessment include unexplained weight loss, a history of cancer, back pain after a significant fall or injury (especially if you have osteoporosis or take long-term steroids), and pain that is severe and constant at night and does not ease with any position.
4. Headache, jaw pain or vision change over 50
Giant cell arteritis (GCA), also called temporal arteritis, is inflammation of blood vessels, most often in the head. It mainly affects people over 50, and some people with it also have polymyalgia rheumatica. The NHS advises asking for an urgent GP appointment or getting help from NHS 111 if you think you might have it, because it can lead to stroke and blindness if not treated quickly.
The NHS lists the main symptoms as frequent, severe headaches; pain or tenderness at the temples or on the scalp; jaw pain while eating or talking; and vision problems, such as double vision or loss of vision in one or both eyes. Read our guide to giant cell arteritis warning signs.
What to do: get same-day help from your GP or NHS 111. Call 999 or go to A&E if you have any loss of vision.
5. Chest pain, breathlessness and blood clots
Some types of arthritis, particularly inflammatory types, are linked with a higher risk of heart and circulation problems, and reduced mobility or recent surgery such as a joint replacement increases the risk of blood clots.
- Call 999 for chest pain, especially if it spreads to the arms, jaw, neck or back; sudden breathlessness; or coughing up blood.
- Get urgent advice from NHS 111 or your GP for pain, swelling and warmth in one leg, usually the calf. The NHS advises calling 999 or going to A&E if you have symptoms of DVT and also feel short of breath or have chest pain, as a clot can travel to the lungs.
6. Signs of a stroke
Use FAST: Face drooping, Arm weakness, Speech problems, Time to call 999. Do not wait to see if symptoms pass.
7. Injuries and falls
Arthritis, some medicines and osteoporosis can increase the risk of falls and fractures. After a fall, get urgent help if you cannot get up or put weight on a leg, a limb looks misshapen, there is severe pain or swelling, or you hit your head and take blood-thinning medicines. Go to an urgent treatment centre or A&E, or call 999 if seriously injured.
8. Medicine side effects that need urgent help
- Stomach bleeding: vomiting blood or material that looks like coffee grounds, or black, tarry stools, particularly if you take anti-inflammatory painkillers or steroids. Call 999 or go to A&E.
- Severe allergic reaction: swelling of the lips, tongue or throat, difficulty breathing, or a sudden widespread rash. Call 999.
- Methotrexate warning signs: the NHS advises telling your doctor or calling 111 immediately for yellowing of the skin or the whites of the eyes; a persistent cough, chest pain or breathlessness; swollen hands, ankles or feet or changes in how often you pee; signs of infection such as a high temperature or sore throat; or bleeding gums, blood in your pee, vomiting blood or unexplained bruising.
- Taking too much of any medicine, for example accidentally taking methotrexate daily instead of weekly: contact NHS 111 or go to A&E, taking the packaging with you.
9. "Something is not right" signs to see your GP about soon
These are not usually emergencies, but should be checked within days to weeks:
- New joint swelling, especially in several joints, or morning stiffness lasting over 30 minutes most days
- Unexplained weight loss, fevers or night sweats
- New stiffness and aching in both shoulders and hips over 50
- Pain that is steadily getting worse despite treatment
- New numbness, tingling or weakness in the hands or feet
- Low mood, hopelessness or thoughts of self-harm (if you feel unable to keep yourself safe, call 999 or go to A&E; Samaritans are available free on 116 123)
How to tell a red flag from a flare
A usual flare feels familiar: the same joints, similar symptoms to previous flares, and no fever or feeling seriously unwell. Red flags are often different: a new pattern, one very hot joint, symptoms elsewhere in the body, or feeling very unwell. If you are not sure, treat it as a red flag and get advice. Our guide on how to identify a true flare explains the difference.
Be prepared
- Keep an up-to-date list of your medicines, doses and allergies in your wallet or phone.
- Carry your steroid emergency card if you have one.
- Save your GP, rheumatology advice line and pharmacy numbers in your phone.
- Write red flags on your flare action plan and share it with family or carers.
- Know where your nearest urgent treatment centre and A&E are.
- Use our emergency arthritis flare checklist to prepare a grab-and-go list.
When to get medical help
- Call 999: chest pain, severe breathlessness, signs of stroke or sepsis, vision loss, collapse, severe allergic reaction, vomiting blood.
- A&E straight away: back pain with cauda equina signs; a hot, swollen joint with fever if you cannot get through to 111 quickly; unable to weight-bear after a fall.
- NHS 111 or same-day GP or rheumatology: infection signs on immune-suppressing medicines; new headache or jaw pain over 50; calf pain and swelling.
- GP within days to weeks: new joint swelling, weight loss, night sweats, steadily worsening pain.
When is joint pain an emergency?
Joint pain is an emergency when one joint suddenly becomes hot, red, swollen and very painful, especially with fever or feeling unwell, as this can be a joint infection. It is also urgent after a fall if you cannot weight-bear or the joint looks misshapen. Call NHS 111 or go to A&E.
What are the red flags for back pain?
Go to A&E immediately for back pain with numbness around the bottom or genitals, problems controlling your bladder or bowels, or weakness in both legs. See a GP promptly for back pain with fever, weight loss, a history of cancer, or after a significant fall.
What should I do if I get a fever while taking methotrexate?
Contact your GP or rheumatology team the same day, or NHS 111 out of hours. Do not stop your medicines without advice. Call 999 if you have signs of sepsis, such as confusion, mottled skin or very fast breathing.
Can a flare cause a fever?
Some inflammatory arthritis flares can make you feel generally unwell or slightly feverish. But a fever, especially with one very hot joint or on immune-suppressing medicines, may be an infection. Do not assume it is a flare; get advice the same day.
Why is a headache a red flag with arthritis?
In people over 50, especially those with polymyalgia rheumatica, a new headache with scalp tenderness, jaw pain on chewing or vision changes can be giant cell arteritis. It needs urgent treatment to prevent sight loss, so get same-day help.
Should I go to A&E or call 111?
Call 999 or go to A&E for life-threatening symptoms. If you are unsure how urgent something is, call NHS 111 or use 111 online. They will assess your symptoms and tell you where to go, and can arrange an urgent appointment if needed.
Sources and further reading
- NHS: Septic arthritis
- NHS: Back pain
- NHS: Giant cell arteritis
- NHS: Sepsis
- NHS: DVT (deep vein thrombosis)
- NHS: Side effects of methotrexate
- NHS: When to use 111
Educational information for people in the United Kingdom — not a diagnosis or personal medical advice. Charity no. 1218461. Pending clinical review. Everyone's situation is different, so always follow the advice of your own GP, pharmacist or rheumatology team. If you feel very unwell, call 999 or go to A&E. For urgent advice, contact NHS 111.
Continue with related help
- Septic arthritis — the hot, swollen joint emergency
- Giant cell arteritis — headache and vision warning signs
- Emergency flare checklist — what to do, step by step
- Is it a true flare? — flare or something else
- Steroid emergency card — if you take steroids
- Flare action plan — printable plan with red flags