Allergy
An allergy is a hypersensitive disorder of the immune system. Allergic reaction occurs when a person’s immune system reacts to normally harmless substances in the environment and produce antibodies. Interaction of antibodies with allergens causes allergic symptoms. The substance that causes a reaction is called allergens.
Many allergens are air borne particles like dust mite or pollen which causes symptoms in areas of contact with air like eyes, nose or lungs.
The reason why a person gets allergic is mainly two
Genetic reason
60% to 80% chance
One parent allergic:
40% to 60% chance
Parents not allergic :
20% chance
Environmental reason
House dust mite, cockroach, cigarette smoke, diesel fumes, ozone, animals, occupation. Outdoor:
Pollens, molds, grasses, weeds
Contact allergy:
Artificial jewellery, latex, leather, hair dyes. o Insect sting allergy eg: Bee sting
Common Allergens
- Dust Mites
- Cockroach
- Pet Dander
- Moulds/Fungus
- Pollens
What are the entry sites of allergens?
Allergen enters into the body mainly by inhalation, ingestion, injection and direct skin contact. Main risk factors for Allergy are:
- Family history of allergies
- Serum IgE>100 IU/ml before age of 6 years
- Animal contact
- Dust mite exposure
- Passive smoking
- Eczema
- Small family size
- Early use of antibiotics
- Western life style
- Diet
Exact mode of genetic transmission is still not known but positive family history is the single most important factor to predict the development of allergies.
What are the symptoms of an allergic reaction?
Common symptoms of an allergic reaction to inhaled or skin allergens include:
- Itchy, watery eyes
- Sneezing
- Itchy, runny nose
- Rashes
- Feeling tired or ill
- Hives (a rash with raised red patches)
How does allergy develop?
The Development of allergies involves IgE Antibodies. It is a two-step process by which individual initially becomes sensitized to a substance.
During the early stage of sensitization, the individual develops significant amount of IgE antibodies against an inhaled, ingested or injected substance. Memory B cells also appear that are capable of immediately producing more of this specific antibodies when stimulated. The second stage involves adherence of this newly formed IgE to circulating Basophils or to the mast cells located in the skin, mucosal surfaces of gastrointestinal tract or respiratory system. The second stage involves adherence of this newly formed IgE to circulating Basophils or to the mast cells located in the skin, mucosal surfaces of gastrointestinal tract or respiratory system. The second step in the two step process of becoming allergic involves the re-exposure of a sensitized person to the same allergen. With exposure production symptoms may vary from mild for example sneezing to sudden death.
What are the types of allergies?
Allergy related diseases can be classified based on the target organs involved. Some common types are mentioned below.
- Nose – allergic rhinitis
- Sneezing
- Lungs -Asthma
- Skin -Dermatitis
- Eye -Conjunctivitis
- Systemic-Anaphylaxis
- Gut -Food allergy
- Ear –otitis media
Why do we need to treat allergies?
In children allergies can progress eg: if allergic rhinitis is not controlled, asthma can develop later. These children are prone for developing recurrent cough, sinus, ear and chest infections. Night time coughs interferes with sleep and thereby causes day time fatigue, sleepiness, poor concentration and school absenteeism thereby interfering with their studies. Exercise induced asthma results in inability to take part in sports. Poor weight gain occurs due to recurrent infections and the final height of the child is affected. In children with skin allergies psychological problems may occur especially due to itching of skin in public. In addition, recurrent hospitalizations causes a huge economic burden in the family. In adults, allergies causes poor quality of life, Interference with work and absenteeism from work.
Allergy skin testing
Allergy skin test is a confirmatory, highly sensitive, reproducible, rapid and cost effective method to screen existing IgE sensitivities that may be responsible for clinical symptoms.
- Skin surface is cleaned with alcohol and dried naturally
- Marking is done on the area of skin test site with a pen
- Then is the application of a small drop of antigen on the site
- A sharp instrument (lancet, hypodermic needle) is passed through the drop and the skin is gently lifted, creating a small break in the skin through which the allergen penetrates.
- Interpretation is done after 15 minutes Factors affecting skin test:
- Age-infancy or old age
- Sex -no difference
- Race-whealing more in blacks
- Circadian rhythm - peaks in late evening
- Seasonal variation - Eg: pollen allergies
- Skin condition-skin eczema
- Other condition-diabetic neuropathy Prerequisites for Skin Testing
- Antihistamines like cetrizine and loratidine, should be stopped at least 5 to 7 days before testing.
- Tricyclic anti depressant (doxepine) and atypical antipsychotic drugs (ex. risperidone, olanzapine, and ziprasidone) should be tapered down, if required, at least 2 weeks before testing. Beta blockers should be stopped in all instances 24 hour before the testing
