Some food allergies cause immediate symptoms whereas in others it takes much longer for symptoms to develop.
The most common type of allergic reaction to food is known as an IgE-mediated food allergy.
In this type of allergy the symptoms develop very quickly after eating the allergy-causing food (the allergen); typically within a few minutes or in some cases, seconds.
Symptoms include:
- a raised red itchy skin rash (urticaria), which can affect just one part of the body, or alternatively, spread across the entire body – in some cases the skin can turn red and itchy but there is no raised rash
- swelling of the face, around the eyes, lips, tongue or the roof of the mouth (angioedema)
- feeling of narrowing in throat
- change in voice (croaky or hoarse) due to swelling in voicebox
- feeling dizzy and lightheaded
- feeling sick
- being sick
- abdominal pain and spasms
- diarrhoea
- cold-like symptoms, such as sneezing, runny nose and nasal congestion
- redness and irritation of the eyes (allergic conjunctivitis)
- coughing
- chest tightness
- wheezing or shortness of breath
In some cases a severe food allergy (anaphylaxis) can be triggered after eating a certain food and then going on to exercise vigorously. This is known as food-dependent exercise-induced anaphylaxis.
A less common type of allergic reaction is known as an non IgE-mediated food allergy. In this type of allergy the symptoms take much longer to develop after eating the allergen; usually several hours or in some cases days.
Some symptoms match what you would expect to see in an allergic reaction, such as:
- redness and itchiness of the skin (although not necessarily raised)
- the skin becomes itchy, red, dry and cracked (atopic eczema)
Other symptoms can be much less obvious and easily mistaken as being caused by something other than an allergy. They include:
- heartburn and indigestion that is caused by stomach acid leaking up out of the stomach (gastro-oesophageal reflux disease)
- stools (poo) becoming much more frequent or loose (though not necessarily "full-blown" diarrhoea)
- blood and mucus in the stools
- in babies: excessive and inconsolable crying even though the baby is well-fed and doesn't need a nappy change (colic)
- constipation
- redness around the anus, rectum and genitals
- unusually pale skin
- failure to grow at the expected rate
Mixed reaction
Some children can have a mixed reaction where they experience both "IgE" symptoms, such as swelling, and "non-IgE" symptoms such as constipation.
This often happens to children who have a milk allergy.
Anaphylaxis
The symptoms of a severe anaphylactic reaction usually develop within a few minutes to an hour after exposure. They can be sudden and rapidly worsen.
Initial symptoms of anaphylaxis are often the same as above and can lead to:
- a rapid heartbeat (tachycardia)
- increasing breathing difficulties due to swelling and tightening of your neck
- a sudden intense feeling of apprehension and fear (this has been described as a "sense of impending doom")
- a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused
- unconsciousness
Anaphylaxis is a medical emergency and, without prompt treatment can be life-threatening.
Dial 999 immediately and ask for an ambulance with a paramedic if you think that you or someone you know is experiencing anaphylaxis.
