When does an allergic rash appear?
A child can come out in an allergic rash anytime during the year; however this occurs most frequently during the warm months of the year, when exposure to various allergens is increased.
What does an allergic rash look like?
Allergic rash usually has some specific characteristics: simple red spots (erythema), or areas of the skin, which are red and slightly elevated in relation to the rest of the skin (wheals), or simple red pimples (papules), causing itchiness. The affected areas may be joined together, and change from time to time. A direct allergic reaction usually lasts from a few hours up to a few days.
Where on the body do they appear?
They can appear anywhere on the body, however, rashes usually appear on the exposed parts of the body, i.e. the neck, the arms, the legs, and the face. In some cases, and depending on the allergen, the reaction is topical, i.e. at the point that came into contact with the harmful agent, while in other cases it is systematic, i.e. it affects the entire body.
Are rashes accompanied by other symptoms?
It is unusual for the child to have a fever – if he does have a fever, it’s possible the rash was caused by an infection, bacteria, or a virus. In the case of an infection, the child may have accompanying symptoms of a virus, such as runny nose, coughing etc.
In some cases, if the rash is severe due to an intense allergic reaction, the child may have swelling in areas of the skin – angioedema –, which could become dangerous, if it is in the facial area, leading to swelling of the larynx and difficulty in breathing, or swelling of the eyelids. Sometimes the allergic reaction is an allergic shock reaction, and the child may have difficulty breathing, be wheezing, or feel generally unwell with a drop in his blood pressure, and go into shock. This is an urgent situation, and immediate medical intervention is required.
What causes allergic rashes?
Allergens from the natural environment (e.g. pollen, caterpillars) may cause immediate and general skin reactions with intense itching in people who are predisposed to allergies.
Contact allergies appear when the child comes into contact with something allergenic, such as insects, plants, synthetic clothing, cosmetic ointments, sunscreens etc. Some of these rashes may also present blisters, i.e. larger pimples containing fluid.
Usually, a rash on the exposed body parts (face, arms, legs) is caused by bites or stings from mosquitoes, bedbugs, bees, wasps etc.
In some cases, the cause of the allergic rash is food-related. This is more likely when the child is of pre-school age, tastes a food for the first time, when pimples appear immediately after the consumption of the food, when there are accompanying gastrointestinal symptoms (vomiting, diarrhea), or when the rash is in the area around the mouth and lips.
Always bear in mind that the rash could be due to photosensitivity, due to intense exposure to the sun, to the use of a medication, or to an infection. A rash that becomes hemorrhagic – doesn’t become white when pressed with the finger, and looks like a bruise – should be immediately evaluated by a doctor.
It is advisable for parents and the doctor to investigate the cause of the allergy in all cases, even though it is not always possible to find a definite cause. Often, the particular allergen only becomes apparent with hindsight, i.e. when the picture is complete after a few days, or after repeated episodes of allergic reaction associated with the same cause.
How is the diagnosis made?
The diagnosis is usually made clinically, from the child’s medical history and a clinical examination. In the case of a severe reaction or relapse, it is advisable to get an evaluation by an allergist, to do a diagnostic check with dermatological tests and/or allergy blood tests (eosinophils, IGE, RAST) aiming to find the specific cause.
How is an allergic rash treated?
In cases of mild or topical rash, the removal of the cause – the allergen – may suffice.
In cases of immediate significant reaction, the use of topical anti-inflammatory medication comprising hydrocortisone helps. Additionally, and in collaboration with the doctor, when the itching is severe, an anti-inflammatory medication by mouth may be prescribed for one or more doses.
With more severe reactions leading to anaphylaxis (anaphylactic shock), parents should seek medical help immediately.
Non-topical administration of cortisone or adrenaline should be carried out only after medical evaluation and supervision. Only those children who are known to be seriously allergic to a particular allergen, and who have been evaluated by an allergist, should carry an adrenaline or cortisone injection. Parents should not obtain these medications without full evaluation by their doctor, and if he decides that they should be used by parents, detailed instructions should be given to them on when and how to use them.
In general, when a child comes out in an allergic rash, try to limit the likelihood of the expansion of the problem. This means that the child could take a bath, but avoiding the use of soap and shampoo, which may dry the skin and irritate it more. Avoid intense exposure to the sun. During the next few days, avoid giving the child new foods that he hasn’t tasted before, or foods that may be allergenic (seafood, egg, chocolate, nuts, etc.). The application of simple moisturizing creams may help.
In the case of bites, there is a risk of contamination. Apply ammonia immediately. If the rash becomes infected, is persistent during the following days, gets redder, and starts to hurt, the doctor may recommend the use of a topical antiseptic or antibacterial ointment.
Stelios Papaventsis MRCPCH DCH IBCLC 2011