Spider bite allergy
Reactions to certain spider bites.
About spider bite allergy
Genuine spider bites are far less common than often assumed, and in the UK most spiders cannot pierce human skin or cause significant harm. When a bite does occur, the local reaction is partly to substances injected by the spider, and, as with other bites, people vary in how strongly they respond. A few UK species, such as the false widow, can give a bite comparable to a bee sting, while medically serious spider venoms are found mainly in other parts of the world. Many blistering skin problems blamed on spiders are actually infections rather than true bites.
Reactions usually appear within minutes to hours and may include pain, redness, swelling and itching around the site, which in most cases settles over a few days. Some bites break the skin and can become infected, showing increasing pain, spreading redness, warmth or pus. Marked or whole-body allergic reactions to UK spider bites are uncommon, though pain and local swelling can occasionally be more pronounced.
Management centres on cleaning the area, relieving discomfort and watching for signs of infection. Keeping the bite clean, avoiding scratching and using measures suggested by a pharmacist can help, and a GP should be consulted if the area becomes infected, blisters, or symptoms worsen. If bitten abroad by a spider known to be dangerous, urgent local medical advice should be sought. A rare severe reaction with widespread swelling, breathing difficulty or collapse is a medical emergency requiring 999.
Common triggers
- Spider bite and products containing it
Symptoms
- Pain, redness and swelling at the sting or bite
- Widespread hives or itching
- Swelling of the face, lips or throat
- Wheezing or difficulty breathing
- Anaphylaxis in severe cases
Avoidance & management
- Avoid nests, hives and known habitats
- Wear covering clothing and avoid strong scents outdoors
- Use insect repellent and screens
- Carry an adrenaline auto-injector if prescribed
- Seek urgent help for a severe reaction
Sources & references
Allergy safety: what everyone should know
Mild-to-moderate reaction signs
- Itching, hives or a raised rash
- Swelling of lips, face or eyes
- Tingling mouth, sneezing, runny nose
- Stomach pain, nausea or vomiting
Anaphylaxis — call 999 (UK) or 112 (EU) immediately
- Difficult or noisy breathing, wheeze, persistent cough
- Swelling of the tongue or tightness in the throat
- Dizziness, collapse, pale and floppy (young children)
- Use an adrenaline auto-injector (e.g. EpiPen) at once if prescribed, then call an ambulance even if symptoms improve
Allergy or intolerance? A true allergy involves the immune system and can escalate quickly; an intolerance (e.g. lactose intolerance) is unpleasant but not life-threatening. The symptoms overlap, so self-diagnosis is unreliable.
Getting tested: home-testing kits based on IgG are not diagnostically valid. If you suspect an allergy, ask a GP for referral to an allergy clinic for skin-prick or specific-IgE testing and a supervised food challenge where appropriate.