Understanding Allergies and Hypersensitivity?

Allergies Clinics of London

What is Allergic Hypersensitivity?

Allergic Hypersensitivity simply put, is an adverse immune reaction to a protein (or allergen) in our environment, which is normally harmless to the non-allergic person.

It may present as mild itching of the skin, tissue swelling and wheezing or even progress to full-blown anaphylaxis and death. Only a small proportion of the population exposed to an allergen will develop an allergic reaction.

"Non-allergic" hypersensitivity reactions are those reproducible adverse reactions that do not involve the immune system. Heart palpitations triggered by caffeine are a good example of a non-allergic hypersensitivity (or intolerance reaction).

Allergy develops after repeated exposure to the causative allergen. Sensitisation takes place on initial exposure (a process that may take up to 6 weeks to develop) and no adverse reaction appears to occur during this sensitisation. Some time later on repeated allergen exposure, the full-blown allergic reaction will occur.

During sensitisation, Immunoglobulin E (IgE) antibodies are produced by our white blood cells and on re-exposure these IgE antibodies bind the allergen and attach to Mast Cells, which release Histamine. This triggers the beginning of the Allergic Reaction, which may manifest anything from a mild itch to anaphylaxis and death. Late phase reactions also may follow 6 to 24 hours later with Inflammation and tissue swelling.

Some people may become sensitised to an allergen and have positive allergy tests but not ever had an allergic reaction. This is called "Latent Allergy" and has no ill effects. These people go about their lives completely oblivious to this fact.

Common Allergic Manifestations include Asthma, Allergic Rhinitis or Hayfever, Atopic Eczema, Urticaria or Hives, Food Allergy, Allergic Conjunctivitis, Wasp Venom Allergy and allergy to Medication such as Penicillin.

What constitutes a good allergy practitioner?

The Practitioner (doctor or nurse) needs to have plenty of time available for the consultation and a keen interest in allergy is paramount. In Allergology (the study of Allergy) the patient’s description of their allergy and careful questioning by the doctor goes 90% of the way to a correct diagnosis. This is usually followed by a brief examination of the relevant organs such as nose, eyes, lungs, glands and skin. Allergy tests should only be done to confirm the suspected allergy detected from the history. Tests should not be used as blind searches for an allergic component to the patient’s symptoms.

Once diagnosed, the patient needs to have the implications of their allergy explained to them in detail. They should be given some "easy to read" educational booklets to take home and digest. Understanding the nature and causes of the allergy will make future allergy control by the patient much more successful. A follow-up consultation is important as it provides an opportunity to discuss problems associated with the allergy and to reinforce the need for treatment.

What are those telltale signs that alert the doctor to probable allergy as the patient walks in the surgery door?

Allergic shiners are often a give-away – these are darkened areas of skin around the eye sockets, which are a result of increased venous congestion in the sinuses. They often resemble "Black Eyes" or look like "Mascara" around the eyes. There may be characteristic Dennie-Morgan infra-orbital folds or linear creases under the eyelids. The typical transverse nasal crease across the bridge of the nose is from constant nose itching and rubbing. The "allergic salute" is seen when the person’s hand constantly rubs the nose and is associated with facial grimacing or so called "Pulling of Faces" because the nose, eyes and ears are so itchy.

After many years of Nasal Allergy, the sufferer develops a so-called "Long Faced" appearance with constant open-mouth breathing, nose blockage, a high arched palate and dental malocclusion with "Buck Teeth".

The allergy sufferer’s skin has a dry and rough sandpaper like texture which is called Keratosis Pilaris. In children, this is commonly associated with eczematous rashes on the face, in the elbow creases and behind the knees. In adults Eczema tends to affect other areas such as the neck, wrists and back of hands.

The nose’s internal mucus membranes are usually swollen and oedematous with a pale blue appearance. The lower-eyelid conjunctival lining has a thickened "cobblestone" appearance and the eyes may be red, watery and itchy. Chronic middle ear mucus or Glue ear often accompanies nasal allergies. Other common allergic manifestations are a wheezy chest, constant sneezing, itchy watery eyes and "Nettle " rashes on the skin.

Written by Dr Adrian Morris Click here for the Surrey Allergy Clinic.

September 2006

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