Causes Of Allergic Reactions

Causes of Allergic Reactions
causes of allergic reactions little girl with arm rash

Learn the different causes of allergic reactions

There are many different causes of allergic reactions including food sources medication, bee or wasp sting venom, pollens, animals or different chemicals.

Allergies can occur at any point in our lives, but the prevalence of the different causes changes with age. For instance, in childhood, particularly when children are first being exposed to a food, allergies are more likely to happen.

Food allergies can persist into adulthood and certainly arise for the first time, but they are more likely in children. As a contrast, allergic reactions to medication are much more likely to occur in adults as are bee and wasp allergies.

Underlying causes

Sometimes, individuals develop signs and symptoms which look as though they may have been caused by an allergic reaction. The commonest things which can occur are urticaria (hives or a nettle sting like rash) or angioedema (swelling). Less commonly, anaphylaxis can also occur. 

When these signs and symptoms develop, naturally everyone looks to find out the underlying cause. Typically, these reactions often begin in the middle of the night and doctors will then usually ask you what you ate for dinner that evening.

This is a red herring as allergic reactions causing hives and swelling tend to occur within minutes to an hour or two of exposure to the food, not hours later whilst asleep.

It is often obvious to me, as an allergy specialist, that if someone is keeping a food diary of what they eat, because of their recurrent hives and swelling, then in all likelihood, these reactions are spontaneous.

skin allergy reaction test person s arm scaled

Viruses and bacteria

Up to 10% of the population, at some point in their lifetime, may have episodes of hives and swelling without an allergic trigger.

In childhood, it is very commonly caused by various viruses and bacteria that they are exposed to.

Quite often, children are misdiagnosed with an antibiotic allergy (which is quite unusual in childhood), when in fact the hives and swelling have occurred either because of the underlying illness or because of interactions between the illness and the antibiotics.

These types of reactions would usually settle within days to weeks and in fact Covid 19 commonly triggers this in adults and children.

Autoimmune systems

If these reactions persist for longer than six weeks, they tend to be termed Chronic Spontaneous Urticaria and Angioedema. As the name might suggest, the cause of this is unknown and there is no underlying allergic trigger.

It is thought that up to 50% of these conditions are autoimmune, i.e. the body triggering these reactions themselves. In an allergic reaction, the exposure of the body to an allergen (something which triggers a reaction like sesame), will cause this allergen, to bind with the immune cell IgE.

Together, this complex will bind onto a cell known as the mass cell. When the mass cell breaks down it releases histamine and other chemicals, and this is what triggers the allergic symptoms which we see. In spontaneous urticaria and angioedema, and in those with spontaneous anaphylaxis, these mast cells will be breaking down without an external source.

There will be regular release of histamine which will mean that hives and swelling will often present for many days or weeks and keep occurring without the same trigger.

There are unfortunately no tests to diagnose this condition, and a good understanding by the medical expert and the recognition of the pattern, is what is needed. For more information please do see our webpage.

Identifying patterns

When there is a clear allergic reaction, there will be an obvious pattern of exposure.

For instance, if someone has an allergy to milk, every time they are exposed to milk, very quickly within minutes to hours their symptoms will develop.

When the milk is removed, their symptoms will resolve quickly would certainly not occur again until exposure happens. It will be this lack of a clear history of exposure to the same allergen, which helps with the diagnosis of spontaneous urticaria and angioedema.

If you need any help in diagnosing the cause of your symptoms or investigating possible allergies, these do contact us or join our free support group.

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Dr Helen Allergy
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