Allergies

The exaggerated response of the immune system to certain antigens present in the environment is called an allergy.

The substance that triggers an allergic immune response in a sensitive individual is called an allergen.

An allergy is the exaggerated response of the immune system to certain antigens present in the environment. The substances that produce such an immune response are called allergens. The antibodies formed in this response are of IgE type.

Common allergens:

• Common allergens include dust mites, pollen, and animal dander.
• Allergens are usually foreign proteins.
• In some cases, drugs and certain other substances may also cause allergic reactions.

Mechanism:

• An allergy occurs due to the release of histamine and serotonin, or similar substances, by mast cells.
• Histamine is present in a bound state in mast cells in tissues and in basophils in the blood.
• When these chemicals are released, allergic manifestations appear rapidly.

Histamine receptors:

• There are two types of histamine receptors in the body: H1 and H2.
• Stimulation of H1 receptors produces allergic manifestations.
• H1 receptors are mainly present in the skin, lung tissue, and intestinal mucosa.
• H2 receptors are present in the gastric mucosa of the stomach.
• Their stimulation increases gastric acid secretion.

Symptoms:

• Common symptoms include sneezing, watery eyes, a runny nose, and difficulty breathing.
• Other manifestations include itching, skin eruptions, urticaria, allergic dermatitis, allergic rhinitis, wheezing, and asthma.
• Redness and watering of the eyes may occur in allergic conjunctivitis.
• In some cases, gastrointestinal colics, vomiting, and diarrhoea are also seen.
• Allergic reactions are usually very rapid.

Diagnosis:

The cause of an allergy is identified by exposing the patient to, or injecting very small doses of, potential allergens and then studying the reactions.

Treatment:

• Drugs such as antihistamines, adrenaline, and steroids quickly reduce allergy symptoms.
• Antihistamines act by blocking the action of histamine in circulation.
• They compete with histamine for H1 receptors and block histamine's action.
• Sodium cromoglycate is an important anti-allergic drug, especially used in respiratory allergy.
• It acts by preventing the release of histamine from mast cells.
• The best treatment is avoidance of the cause when the cause is known.

• Anaphylactic shock is a severe acute emergency in which a person develops shock after injection of a foreign protein, even in a very small amount, due to sensitisation from a previous dose.
• A similar reaction may occur when an antigen enters the bloodstream, as in a bee sting or wasp sting, and spreads rapidly to mast cells throughout the body.
• This causes the simultaneous discharge of large quantities of histamine.
• Wheals may develop all over the skin within a minute or two.
• The face, lips, and tissues around the eyes may swell markedly, and the throat may feel thick due to swelling around the tongue and mouth.
• There is a massive drop in blood pressure, the heart rate becomes rapid, and the person may faint.

• The modern lifestyle has lowered immunity and increased sensitivity to allergens.
• More children in metro cities suffer from allergies and asthma because of sensitivity to the environment.
• This is mainly linked with the protected environment provided early in life.

• An allergy is an exaggerated immune response to environmental antigens.
• IgE is the antibody involved in allergic reactions.
• Histamine and serotonin released from mast cells are responsible for allergic symptoms.
• H1 receptors are related to allergic manifestations, whereas H2 receptors are related to gastric acid secretion.
• Severe systemic allergy is called anaphylactic shock.
• Diagnosis is done by testing with small doses of allergens.
• Antihistamines, adrenaline, steroids, and sodium cromoglycate are used in treatment.