Allergy can be simply defined as an undesirable, idiosyncratic reaction to a substance that is mediated via the immune system. The skin is probably one of the most common organs where allergic reactions manifest.
Allergic reactions on the skin can be broadly divided into immediate allergies and delayed allergies. Immediate type allergic reactions occur rapidly( usually within minutes to hours) after exposure to the allergenic substance, whereas delayed type allergic reactions occur days or weeks after exposure. A common erroneous assumption is that one cannot be allergic to something he or she has been taking or using for a period of time. This is untrue. Allergies, in fact, can still occur after the body has been exposed to a particular substance for a period of time, or after multiple exposures to a substance.
Below are some common allergic skin reactions:
Contact dermatitis is an allergic reaction caused by substances IN CONTACT with the skin. Contact dermatitis usually appears as a red itchy rash. In more severe reactions, blisters and swelling may also occur. Some classic examples of contact dermatitis include: itch and redness over the earlobe caused by allergy to nickel in metal earrings; itchy rash over the scalp and/or face and ears caused by allergy to permanent hair dyes; itchy rashes on the face due to allergy to certain ingredients in skin care products; itchy rashes on the feet due to allergy to the rubber or leather material in footwear.
Substances that are well known to cause contact allergies are hair dyes, metals, rubber chemicals, leather, fragrances, certain preservatives ( eg formaldehyde, parabens), epoxy resin, certain medicaments( eg certain topical antibiotics, anaesthetics and anti-inflammatory gels).
The exact cause of contact allergies can be confirmed by PATCH TESTING.
Drug allergies Drugs can cause allergic reactions. They most commonly manifest as a red itchy rash on the body. Other symptoms that may occur in the setting of an allergic drug reaction include:
- Angioedema( swelling of the eyes or mouth or face)
- Blisters on the skin
- Broken skin( erosions)
- Sun sensitivity
- Few discrete red circular spots on the skin ( otherwise known as ”fixed drug eruption”)
Although most allergic drug reactions are not serious, and can be simply treated by stopping the drug and taking some symptomatic treatment, there are a few allergic drug reactions that are potentially very serious and may be life-threatening. One form of severe allergic drug reaction is called Steven Johnsons syndrome or Toxic epidermal necrolysis. In this condition, one develops painful blisters and broken skin affecting large areas of the body. The appearance of the skin is often liken to the effect of suffering from burns. Often, the mouth is ulcerated causing severe pain and difficulty in eating.
Another form of severe allergic drug reaction is called anaphylaxis. Anaphylaxis occurs within minutes to hours after taking the drug. In this condition, the person often develops widespread hives, swelling of the face/eyes/ lips/tongue, together with breathing difficulty and giddiness. Other symptoms include difficulty swallowing, feeling of a lump in the throat, stomach cramps, feeling cold and clammy. If emergency medical attention is not sought, anaphylaxis can be life-threatening.
Drug allergy testing is usually not required if the culprit drug is obvious. However, allergy testing may be necessary if there is uncertainty if the skin reaction was indeed caused by a drug allergy, or if the person was multiple drugs at the time of the reaction and it is unclear which drug was the cause of the allergy. There are different forms of drug allergy testing including blood tests, skin tests and drug challenge testing.
Food allergies are caused by the immune system over-reacting to a particular protein found in the food. Food allergies occur most frequently in young children. Allergic reactions to foods usually occur within minutes to hours of eating the particular food.
Symptoms of a food allergy include:
- Angioedema (swelling of the lips, tongue or eyes)
- Stomach cramps, vomiting or diarrhoea
Food allergies can also result in a severe reaction called anaphylaxis. Some signs of anaphylaxis include: widespread hives, swelling of the face and/or eyes, giddiness, feeling cold and clamy, difficulty breathing, wheezing, difficulty swallowing.
The more common causes of food allergies are:
- Cow’s milk
- Tree nuts( eg walnuts, pinenuts, peacans, pistachios)
Allergy testing in the form of blood test and skin prick test can be done to confirm the exact cause of a suspected food allergy.