Causes Of Hives Urticaria

Causes of hives; not always an allergy!

It is human nature when one develops hives or a nettle sting like rash, to wonder if an allergy has caused it.

Indeed, many doctors who are not trained in allergy, will often think that when patients present to the emergency department or to their GP, with widespread hives, that an allergy has triggered it. In fact, this is not always the case.

causes of hives uticaria girls arm with blotches

When allergic reactions occur, they can trigger hives or other symptoms such as swelling, vomiting, diarrhoea, abdominal pain, runny nose, runny eyes or anaphylaxis; this is called an IgE allergy.

These types of allergic reactions are usually very obvious. They can occur at any point through our lives although most commonly, they arise in childhood.

When a person is exposed to the allergen or thing that they are allergic to, they rapidly develop their allergic symptoms. This can be in response to food, medications, bee or wasp sting venom, pollens or animals.

They occur rapidly and will occur with each subsequent exposure to the same thing. Crucially, they also clear from the body within an hour or two.

While some patients with allergies have what is termed a biphasic reaction (a secondary response which can occur anywhere from 4 to 72 hours later), this is not common.

Anyone who has hives and /or swelling, which is randomly occurring without a clear pattern of trigger, will often have a nonallergic course.

No cause can be found for the causes of hives

For individuals where the hives have lasted for longer than six weeks, no cause is often found. Within our body there are cells called mast cells which contain histamine and other chemicals. In an allergic reaction, a trigger will cause these to break down. For those without a pattern, these cells are being broken down frequently but for no apparent reason.


This tends to leave individuals with hives and sometimes swelling and even rarely symptoms of anaphylaxis which can last for days and weeks at a time. The history of this is always very different from that of an allergic reaction. It is thought that in around 50% of individuals there is an association with autoimmune conditions.

This is when the body has triggering off a response against its own cells causing the breakdown of mast cells. There may be a link with other autoimmune such as thyroid disease or rheumatoid arthritis. There may be a family history of similar.

Pressure uticaria

Some individuals with urticaria (hives) and angioedema (swelling) may have cholinergic urticaria which is triggered by exercise. Pressure urticaria develops for some and they get swelling at sites where pressure has been applied to the body, such as around bra straps or waistbands. Probably not one of the causes of hives you would have thought of.

Some individuals have hives triggered by water, heat or cold. It is important that these triggers are recognised as they can cause significant symptoms and impact on quality of life.


In children, the commonest reason for developing hives which last for days or weeks is in response to an illness. Covid 19 causes rashes including urticaria (hives) in up to 25% of people.

This is sometimes the first sign of the illness. In some children it will be obvious they are unwell as they may have a fever, cough, runny nose or tummy bug.

In other children the rash may be the only sign of the illness just like with chickenpox. Is also very common in children who are unwell to be given antibiotics and then develop hives, not because of an antibiotic allergy, but because of the illness itself or because of interactions of the illness with the antibiotic.

Children are then commonly mislabelled with an antibiotic allergy, and it is crucial an expert in allergy is consulted, to avoid diagnostic errors.

We all recognise that this can of course be challenging as allergy knowledge is sometimes limited in primary care and with some hospital doctors.

There are many treatments which exist to help with these conditions and often they can be easily accessed without the need for a specialist hospital referral.

Many patients seek an expert allergy opinion thinking allergy tests are necessary, but they invariably bring back negative results. Allergies are not the cause of their symptoms and will not stop the hives from occurring.

Dr Helen Allergy is an expert at assessing causes of recurrent hives and swelling and would be happy to help if further information is needed.

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