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Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Yes, usually. A doctor can assess a rash, hives or swelling on camera, find the likely trigger and prescribe; breathing problems or throat swelling need emergency care.
- What it is: the immune system overreacting to something normally harmless, such as a food, medicine, sting, pollen or something touching the skin.
- Common signs: hives or an itchy rash, swelling of the lips, eyes or face, sneezing, a runny nose, red, watering eyes, or tummy pain and sickness.
- How long it lasts: hives usually get better within a few days, and each patch fades within 24 hours; a rash from something touching the skin clears once you avoid it.
- Emergency: call 112 for sudden swelling of the lips, mouth, throat or tongue, difficulty breathing or swallowing, or feeling faint.
Do not book a video appointment if your lips, mouth, throat or tongue suddenly swell, you are struggling to breathe or swallow, your throat feels tight, your skin or lips turn blue, grey or pale, or you feel faint, confused or drowsy. This can be anaphylaxis: use an adrenaline auto-injector if you have one and call 112.
Can an online doctor treat an allergic reaction?
Yes, usually. Most allergic reactions, such as hives, an itchy rash or swelling of the lips or eyelids with normal breathing, show clearly on camera and in photos. The doctor works out the likely trigger, recommends or prescribes antihistamines, a steroid cream or a short course of steroid tablets, and explains how to avoid another reaction. Swelling of the throat or tongue, breathing problems or faintness are anaphylaxis, which needs adrenaline and emergency care.
How an online consultation helps with an allergic reaction
- The trigger found: What you ate, took, touched or were stung by, and how the timing fits.
- The right treatment: A non-drowsy antihistamine, a steroid cream for an inflamed rash, or steroid tablets for a severe reaction.
- The danger signs explained: Which symptoms mean anaphylaxis, and what to do if they start.
- Tests when they help: A referral for allergy tests when the trigger is unclear or the reaction was severe.
What the doctor checks in an online consultation for an allergic reaction
The doctor checks for the warning signs of anaphylaxis first, then looks at the reaction and its timing. The doctor asks about:
- Warning signs: swelling of the throat or tongue, a hoarse voice, difficulty breathing or swallowing, or feeling faint.
- The reaction: where it started, whether it itches, burns or stings, whether it moves around, and how long each patch lasts.
- Timing: what you ate, drank, took, touched or used in the hours or days before, including new cosmetics, hair dye and jewellery.
- Medicines: anything new, including antibiotics and anti-inflammatory painkillers such as ibuprofen.
- Earlier reactions: known allergies, hay fever, asthma and eczema, and reactions in the past.
- Your health: pregnancy or breastfeeding, long-term conditions, and the medicines you take.
Before the call, take clear photos of the rash or swelling in good light, because hives can fade within hours, and write down everything new in the day before it started.
What is an allergic reaction?
An allergic reaction is the body reacting to something that is normally harmless, called an allergen, as if it were a threat. The immune system releases chemicals such as histamine, which cause the itching, rash, swelling, sneezing and watering eyes. The common triggers are:
- tree and grass pollen, which causes hay fever
- house dust mites
- foods such as peanuts, milk and eggs; see food allergy
- animals, especially cats and dogs; see pet allergy
- bee and wasp stings
- certain medicines; see penicillin and drug allergy
- substances touching the skin, such as nickel, cosmetics, hair dye and latex
How quickly does an allergic reaction start?
Anything from a few minutes to a few hours after contact. A rash from something touching the skin can take hours or days, and a reaction to hair dye can take up to 72 hours to appear.
What does an idiopathic allergic reaction mean?
Idiopathic means that no cause is found. It is common with hives that keep coming back: chronic spontaneous urticaria is not caused by allergy, and in most people with swelling under the skin, called angioedema, no underlying cause can be found. Sometimes even anaphylaxis has no known trigger.
What does an allergic reaction look like?
Usually an itchy, raised rash of bumps or patches, called hives, swelling of the lips, eyelids or face, or red, itchy, dry skin where something touched it. Sneezing, a runny nose, watering eyes, coughing, or tummy pain and sickness can come with it.
Swipe sideways to compare →
| Type | What you notice | Common triggers |
|---|---|---|
| Hives (urticaria) | Raised, itchy bumps or patches that can sting or burn and move around; each one usually fades in a few hours | Foods, medicines, stings, plants, animals, latex |
| Allergic contact dermatitis | Itchy, dry, cracked or blistered skin where something touched it, often the hands or face | Nickel, cosmetics, hair dye |
| Swelling (angioedema) | Swelling of the lips, eyelids, face, hands or feet, often with hives | Foods, medicines, stings; often no cause found |
| Nose and eyes | Sneezing, a runny or blocked nose, red, itchy, watering eyes | Pollen, dust mites, pets |
| Food reaction | Hives, swelling of the lips, tummy pain, feeling or being sick, diarrhoea | Milk, eggs, peanuts, tree nuts, shellfish, wheat |
| Anaphylaxis | Throat or tongue swelling, difficulty breathing, feeling faint; an emergency | Foods, medicines, stings, latex |
An allergic rash on brown and black skin
Hives look pink or red on white skin, and the colour can be harder to see on brown and black skin, where the raised bumps and the itch are the main clues. A contact rash can look red on lighter skin and dark brown, purple or grey on darker skin.
An allergic reaction on the face
The face reacts easily: swollen lips or eyelids, hives, or an itchy, red, dry rash from cosmetics or hair dye. Swelling of the lips or eyelids with normal breathing can be assessed online. Swelling of the tongue or throat, or a hoarse voice, is an emergency. See angioedema.
How do you tell if a rash is an allergy?
These clues point to an allergic reaction:
- the rash started soon after a new food, medicine, sting, cosmetic or product
- it is very itchy, and raised bumps appear, fade within hours and come up somewhere else
- it comes with swelling of the lips or eyelids, sneezing or watering eyes
- it happens again each time you meet the same trigger
Not every itchy rash is an allergy. Hives can also be set off by cold, heat and sweating, stress, spicy food, pressure from tight clothing, and infections. Rashes from heat, eczema, infections and other skin conditions can look similar, and a doctor can tell them apart on camera. See hives, contact dermatitis, eczema, heat rash and skin rash.
How long does an allergic reaction last?
Hives usually get better within a few days, and each raised patch fades in a few hours. A rash from something touching the skin clears once you avoid the trigger. Hives lasting more than 6 weeks are called chronic, and need a doctor.
Swipe sideways to compare →
| Reaction | Usual course | See a doctor if |
|---|---|---|
| Hives | Each patch fades in a few hours; the rash usually settles within a few days | It is no better after 2 days, spreading, or keeps coming back |
| Hives that keep coming back | More than 6 weeks is chronic urticaria, usually not caused by allergy | Always, for a plan to control it |
| Contact dermatitis | Clears once the trigger is avoided | It is severe, keeps coming back, or the trigger is unclear |
| Hair dye reaction | Can take up to 72 hours to appear | Symptoms do not go away or get worse |
| Anaphylaxis | An emergency, even if the symptoms ease | Call 112 now |
How do you treat an allergic reaction?
Stop or avoid whatever triggered it, and take a non-drowsy antihistamine for itching, hives and sneezing. A steroid cream helps a sore, inflamed contact rash, and a doctor may prescribe steroid tablets for a severe reaction.
What you can do yourself
- Stop the suspected trigger: the food, product, jewellery or cosmetic. If a new medicine might be the cause, speak to a doctor before stopping it.
- After a reaction to hair dye, wash your hair and scalp thoroughly with a mild shampoo straight away.
- Ask a pharmacist about an antihistamine, and mention any long-term condition and the medicines you take.
- Use a moisturising emollient on dry, itchy skin.
- Avoid scratching, tight clothing and getting hot, which can make hives worse.
- Keep a diary of what you ate, used and did before each reaction, to help find the trigger.
Drowsy and non-drowsy antihistamines
Non-drowsy antihistamines, such as cetirizine, fexofenadine and loratadine, are less likely to make you sleepy, so they are usually preferred for allergic rashes. Drowsy ones, such as chlorphenamine, can affect coordination, reaction speed and judgement: do not drive or use machinery after taking them, and avoid alcohol with any antihistamine.
Prescription treatment
A prescription is never issued without a consultation. Depending on the reaction, the doctor may prescribe a stronger antihistamine, a menthol cream for itching, a steroid cream for an inflamed contact rash, or a short course of steroid tablets for a severe or widespread reaction. If the doctor prescribes, use the prescription at a pharmacy near you.
What does not help
An antihistamine in place of adrenaline when there are breathing problems or throat swelling: antihistamines do not treat anaphylaxis. Carrying on with a product that keeps causing a rash. Unproven allergy tests sold online; see allergy testing.
Which treatment might the doctor recommend for an allergic reaction?
Treatment depends on the type of reaction, how severe it is and what triggered it. This is the framework the doctors use:
Swipe sideways to compare →
| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| Throat or tongue swelling, breathing difficulty, or feeling faint | Adrenaline and emergency treatment | No | Call 112 now |
| Hives with normal breathing | Non-drowsy antihistamine and finding the trigger | Yes | If breathing, swallowing or the voice changes |
| Swollen lips or eyelids with normal breathing | Antihistamine, and a check of your medicines | Yes | If the tongue or throat swells |
| An itchy, red rash after hair dye, cosmetics or jewellery | Stop the product, emollient, steroid cream | Yes | Patch testing at a dermatology clinic, if the trigger is unclear |
| A rash after starting a new medicine | Deciding whether to stop it, an alternative, and recording the allergy | Yes | If the rash spreads fast, or you have a high temperature and feel unwell |
| Hives coming back for more than 6 weeks | Regular antihistamine and a plan to control it | Yes | Dermatology care if it stays uncontrolled |
A rash or swelling you think is an allergy? A doctor can look at it and tell you what will settle it in one consultation.
See available times →How to prevent another allergic reaction
- Avoid the trigger once you know it, and read food labels every time if a food is the cause.
- Test a new hair dye on a strand of hair at least 48 hours before you use it, and choose a non-permanent dye if you have reacted to a permanent one.
- Avoid black henna tattoos: the paste contains high levels of PPD, which raises the risk of a reaction to hair dye later on.
- Make sure any reaction to a medicine is written in your health record, and tell every doctor and pharmacist.
- If you have been given adrenaline auto-injectors, carry 2 at all times.
If the trigger is unclear or the reaction was severe, allergy tests can help. See allergy testing.
Special situations
Pregnancy and breastfeeding
Speak to a doctor or pharmacist before taking an antihistamine. Loratadine is usually recommended if you need one in pregnancy, and loratadine or cetirizine are usually fine while breastfeeding.
Older people and long-term conditions
Check with a doctor or pharmacist before taking an antihistamine if you are older, take other medicines, or have heart, liver or kidney disease or epilepsy.
Reactions to medicines
A rash from an antibiotic or an anti-inflammatory painkiller needs a doctor’s view, because it decides which medicines are safe for you in future. See penicillin and drug allergy.
Children
Mobi Doctor consultations are for adults aged 18 and over. A child who is unwell needs a paediatrician or a local doctor in person, and emergency signs in a child mean 112.
When an allergic reaction is treated online, and when you need in-person care
Treated online: hives, itchy rashes, contact rashes, and swelling of the lips, eyelids or face with normal breathing; finding the likely trigger; antihistamines, creams and steroid tablets when needed; and follow-up on photos.
In-person care: anaphylaxis, swelling of the tongue or throat, breathing problems or faintness; patch testing and allergy tests; and rashes that blister, spread fast or come with feeling very unwell.
When to get in-person care
Call 112 or go to an emergency department now for:
- sudden swelling of the lips, mouth, throat or tongue
- breathing very fast or struggling to breathe, wheezing, or a feeling of choking
- a tight throat or difficulty swallowing
- skin, lips or tongue turning blue, grey or pale
- sudden confusion, drowsiness or dizziness, or someone fainting who cannot be woken
Get medical advice the same day for:
- hives or a rash that is no better after 2 days, or is spreading
- swelling under the skin, of the lips, eyelids, hands or feet
- a rash with a high temperature and feeling unwell
- hives that keep coming back
How Mobi Doctor works
- Book a time that suits you: daily 7am–11pm CEST. You can see a doctor over video, usually within 15 minutes. No subscription, and the exact price is shown before you pay.
- Speak to a licensed doctor about the reaction: show the rash or swelling on camera and say what was new in the day before it started.
- Leave with a plan: what to take and for how long, what to avoid, and which signs mean you should be seen in person. If the doctor prescribes, use the prescription at a pharmacy near you.
No sign-up needed
A rash, hives or swelling can have more than one cause. Tick every symptom you have to see each condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call. If you have an emergency sign listed on this page, call 112 instead.
Tap the body — an area or a point — to browse symptoms anywhere
Similar symptoms, different condition? Hives can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about allergic reactions
What does an allergic reaction look like?
An allergic reaction usually looks like raised, itchy bumps or patches called hives, swelling of the lips, eyelids or face, or an itchy, red, dry rash where something touched the skin. Sneezing and watering eyes can come with it.
How do you tell if a rash is an allergy?
An allergic rash usually starts soon after a new food, medicine, sting or product, is very itchy, and comes back with the same trigger. Hives that fade within hours and appear elsewhere are typical.
How long does an allergic reaction last?
Hives from an allergic reaction usually get better within a few days, and each patch fades in a few hours. A contact rash clears once you avoid the trigger. Hives lasting more than 6 weeks are chronic and need a doctor.
How do I get rid of an allergic reaction rash?
To settle an allergic reaction rash, avoid the trigger and take a non-drowsy antihistamine. A moisturising emollient helps dry skin, and a doctor may prescribe a steroid cream or tablets for a severe or inflamed rash.
What can I do at home for a mild allergic reaction?
Stop contact with the likely trigger, take a non-drowsy antihistamine such as cetirizine or loratadine, cool the skin with a cold flannel or a cool shower, and wear loose cotton clothes; a moisturising emollient soothes a dry, itchy contact rash, and a note of what you ate, took or touched in the hours before helps a doctor find the cause. Avoid scratching, hot baths and alcohol, which make hives worse, and get help without delay if swelling spreads to the mouth or throat.
What does an idiopathic allergic reaction mean?
That no cause is found. It is common with hives that keep coming back and with swelling under the skin, which are often not caused by allergy at all.
How long after contact does an allergic reaction start?
From a few minutes to a few hours. A rash from something touching the skin can take hours or days, and a hair dye reaction up to 72 hours.
Which antihistamine is best for an allergic reaction?
For an allergic reaction, a non-drowsy antihistamine such as cetirizine, fexofenadine or loratadine, is usually preferred because it is less likely to make you sleepy. A pharmacist can help you choose.
Can stress cause hives?
Yes. Emotional stress, heat, sweating, cold, pressure on the skin, exercise and infections can all set off hives without any allergy, because the skin releases histamine in response to them. These hives look the same as an allergic reaction and respond to the same non-drowsy antihistamines, and hives that keep coming back for more than 6 weeks are called chronic and need a doctor to look for the pattern.
When is an allergic reaction an emergency?
An allergic reaction is an emergency when the lips, mouth, throat or tongue suddenly swell, breathing or swallowing is difficult, or someone feels faint, confused or very drowsy. Call 112 and use an adrenaline auto-injector if there is one.
Can I take an antihistamine in pregnancy?
Speak to a doctor or pharmacist first about an allergic reaction in pregnancy. Loratadine is usually recommended if you need an antihistamine in pregnancy, and loratadine or cetirizine are usually fine while breastfeeding.
Will a doctor prescribe steroids for an allergic reaction?
Sometimes. A steroid cream helps an inflamed contact rash, and a short course of steroid tablets may be prescribed for a severe or widespread reaction.
Can an online doctor treat an allergic reaction?
Yes, usually. A doctor can assess an allergic reaction, a rash, hives or swelling, on camera, find the likely trigger and prescribe treatment. Breathing problems or throat swelling need emergency care.
- Allergies, NHS, National Health Service (UK), reviewed 5 March 2026.
- Hives, NHS, National Health Service (UK), reviewed 26 April 2024.
- Urticaria and angioedema, Allergy UK, national charity, accessed 15 October 2026.
- Contact dermatitis, NHS, National Health Service (UK), reviewed 3 May 2023.
- Hair dye reactions, NHS, National Health Service (UK), reviewed 29 December 2025.
- Antihistamines, NHS, National Health Service (UK), reviewed 16 May 2023.
- Anaphylaxis, NHS, National Health Service (UK), reviewed 21 June 2023.
- Emergency treatment of anaphylaxis, Resuscitation Council UK, guideline, May 2021.
- Food allergy, NHS, National Health Service (UK), reviewed 20 August 2026.
- Food allergy and food intolerance testing, BDA, British Dietetic Association, food fact sheet, August 2026.
- Drug allergy: diagnosis and management (CG183), NICE, National Institute for Health and Care Excellence, published September 2014.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
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