Allergic conditions have become one of the leading health concerns today. Whether due to the life style, increasing hygienic conditions, vaccinations or other reasons, cases of allergy coming to the clinic are not so infrequent these days. Some of the common allergens encountered in our day to day practice includes House dust, Mites, Animal dander, Pollens, Molds, Drugs, Food items (such as Peanuts, Soy) etc. Some people also develop allergies from hot or cold temperature, sunlight or sometimes to friction (rubbing or stroking the skin).

‘Inappropriate’ refers to the immune reactions misdirected towards one’s own immune system leading to conditions, E.g. Auto immune diseases. Examples of exaggerated immune response may include Atopy and Anaphylaxis.

Coombs and Gell (1963) classified allergic or hypersensitive reactions into four types based on their different mechanism of pathogenesis:

Type I - Also known as immediate hypersensitivity. These are Ig-E mediated.  In type I reactions Antigen binds to IgE antibodies triggering release and synthesis of mediators (such as histamine, proteases, chemotactic factors, prostaglandins, cytokines) leading to the clinical response. These reactions take less than an hour to develop after an exposure.

E.g. of Type I reactions may include Atopic disorders ( E.g. allergic asthma, allergic rhinitis, Conjunctivitis), Anaphylaxis, Angioedema, Urticaria, Latex and Food allergies.

Type II -  Also known as cytotoxic reaction. Type II reactions are initiated by the IgG (or IgM sometimes) antibodies that react either with cell surface or tissue antigens. Antibody bind to the cellular or tissue antigens or to a molecule coupled to a cell or tissue, leading to cell or tissue damage by complement system or mononuclear cells.

E.g. of Type II reactions may include Hyperacute graft rejection, Hashimotos thyroiditis, Anti-glomerular basement membrane Disease (E.g. Good pasture’s syndrome)

Type  III -  Also known as Immune complex or Toxic complex disease. In Type III reaction acute inflammation occurs in response to circulating antigen-antibody immune complexes deposited in the vessels or tissue. These complexes activate certain immune cells, causing release of inflammatory mediators.

E.g. of Type III reactions may include SLE, RA.

Type IV - Also known as Delayed or cell mediated hypersensivity. In Type IV reaction the T cells sensitised after a first exposure are activated by re-exposure to the same antigen; they damage tissue by direct toxic effects or through release of cytokines which activate eosinophiles, monocytes, macrophages, neutrophiles or killer cells.

E.g. of Type IV reactions may include Contact dermatitis, TB, Allograft rejection, Drug hypersensitivity.

The first exposure of an harmless exogenous substance may lead to production of specific IgE antibodies by activated B cells. These antibodies binds to the surface of mast cells via IgE receptors.  Upon re-exposure the allergen binds to the membrane bound IgE which sensitises the  mast cells and basophils, which then release a variety of vasoactive mediators causing Type I reaction. Among these Histamine is an important vasoactive amine in pathogenesis of human anaphylaxis. Histamine is released from the intracellular granules into the skin. It stimulates the sensory nerves, producing burning and itching sensation. It causes vasodilatation and hyperaemia by an axon reflex and oedema by increasing capillary permeability. It also induces smooth muscle contraction in tissues and organs including vasculatures, intestines, uterus, and bronchioles and stimulates secretions. It acts along with other mediators like Serotonin, Chemotactic factors, cytokines, interleukins, prostaglandins.

Persistent activation of mast cells leads to recruitment of other cells to the site of release. An Early phase response is followed 4-8 hours later by swelling and local inflammation known as late phase reaction mediated by basophils, eosinphils and macrophages. Recurrent allergic inflammation may give rise to chronic inflammatory response including a complex infiltrate of macrophages, eosinophils, T lymphocytes, mast cells and basophils.

Symptoms depend on the part of body coming in contact with the allergen or the route allergen enters into the body:

Some of the commonly seen allergic symptoms include:

Respiratory symptoms include:

Gastro-intestinal symptoms include:

Skin symptoms may include:

Also Acute allergic conditions as Anaphylactic  reaction can be severe and life threatening.

Symptoms of Anaphylaxis can include:

Clinical evaluation- History – Past and Family history may direct a case towards allergic condition. 

Blood Tests – Allergic patients may show Increased Serum IgE levels  and increased Eosinophil count

Skin testing

Radioallergosorbent (RAST) Tests – These are specific IgE tests. These are useful in cases of patients on anti-histamines, uncooperative, having dermatographism or severe generalized skin disease.

Case I

Mr. S. L. W. got conjunctivitis with much redness of the left eye and lachrymation. He was advised by an eye-specialist to use Penicillin eye-drops (2000 units per c.c. ) every hour. Next morning he woke up to find much oedematous swelling of the upper eyelid, lower lid and part of the cheek with inflammation, itching and oozing of a watery fluid from the affected area. I was called to see him and do something. As I had seen three similar cases of Penicillin allergy before. I at once asked him if he had been using the famous wonder drug locally. "Oh yes, but how could you know this?", was his surprised exclamation. "I myself feel it is due to Penicillin," he continued, "but the same eye-specialist says it is not so, that it is due to contact of acrid eye-discharge with the surrounding skin, and that I should take Penicillin injections, one lac units every 3 hours." He was put on Apis mel. 30. t.i. d., and the next day he was a little better. But he was very nervous and anxious, and his several old school doctor friends persuaded him to try allopathic treatment, promising a quicker cure. They treated him with Antistine, Benadryl, Calcium and Vitamin B injections, and it took him about three weeks to come round.