Allergens are inciting agents of allergy i.e the substances capable of sensitizing the body in such a way that an unusual response occurs in hypersensitive person.
Allergen may be biologic, chemical, or of synthetic origin. Example: Pollens, danders, dust, etc.., the chemical identity of allergen is unknown. But most known allergens are protein or glycoprotein and do not have much difference from other immunogens except perhaps being somewhat smaller in size (mol wt. 10,000-70,000). A number of low molecular weight chemicals (allergenic haptens) are partial immunogens and induce allergy after combining covalently with a suitable protein carrier, viz drug allergy.
What is an Allergy?
The allergy (hypersensitivity) may be defined as a specific immunologic reaction to an immunogen – A normally harmless substance (allergen).
It was first defined in 1906 by Von Pirquet who described allergy as a changed or altered reaction in the body of an individual, in response to a substance or condition that is harmless to others.
The occurrence of allergic diseases is determined by the characteristic of the individual as well as those of the allergen and even the condition of exposure.
- Sneezing – Symptom of a cold, but sometimes allergic reaction to something in the air.
- Insect bites and stings.
- Red, itchy, watery eyes.
- Red itchy rash on the skin.
Types of Allergens
The allergens are classified into 5 types on the bases types of symptoms:
1. Inhalant Allergens
Inhalant allergens are airborne substances as chemicals, causing respiratory disease, inflammation in the nose, and lungs.
Inflammation in the nose is manifested by a condition called Sinusitis or hay fever.
Inflammation of lungs is often expressed as asthma.
Symptoms of allergens to airborne substances are:
- Coughing and postnasal drip.
- Itching eyes, nose, and throat.
- Sneezing often accompanied by a runny or clogged nose.
- Allergic Shiner (dark circle under the eyes caused by increase blood flow near the sinuses).
- The ‘Allergic salute’ (in a child, persistent upward rubbing of the nose that causes mark on the nose).
- Watering eyes, conjunctivitis.
How does Inhalant Allergen effect
Once the allergens land on the inner lining of the nose, a chain reaction occurs, which leads to release in the histamine (mast cells) and other chemicals. These powerful chemicals contract some of the small blood vessels on the nose. Which allows fluid to escape causing the nasal passage to swell resulting in nasal congestions.
Example of Inhalant Allergen
- Mould Spores
- Animal Allergy (epidermis, or dander).
2. Ingestant Allergens
Allergens that are present in foodstuff and swallowed are termed as Ingestant (food allergy).
A food allergy is an immune system response to a food. Once the immune system decides that a particular food is harmful, it creates a specific antibody to it.
Symptoms that are caused by Food Allergens are:
- Skin rash.
- Puffed lips and tongue.
- Severe Eczema of hand and feet.
Note: The effect of food allergens is not localized to one organ or area of the body but it may transfer to another organ by blood.
How does the Food Allergen effect
Milk (Dairy) allergy is a specific immunologic antibody-antigen reaction due to lactalbumin because heating and boiling alter this protein which results in severe dermatitis, recurrent rhinorrhea, bronchitis, and asthma.
Example for Food Allergens:
- Peanut, tree nuts (cashew nut, walnut).
- Orange Juice
- Cod liver oil or other vitamins containing fish liver oils.
- Food additives like artificial preservatives, artificial colors, Gluten, potato starch, etc…
3. Injectant Allergens
When a person is subjected to any antibiotic injection that is hypersensitive to the body it causes Injectant allergy. It can also be caused by natural sources like insects sting.
Symptoms caused by Injectant Allergens are similar to those of antibiotics (like Pensulin, cephalosporin, etc).
- Itching of palms of the hands and soles of the feet.
- Peeling of the skin.
Note: In severe cases, anaphylactic shock may occur.
- The sting of bees.
- Injectable liver extract, Antitoxins, Glandular Products.
- Vaccines for different diseases.
4. Contactant Allergens
A number of plants and their products have been identified as the causes of contact allergies.
Symptoms of Contactant Allergens are:
- Contact Dermatitis caused by the Anacardiaceae family, Compositae family.
- Snow on the mountain.
- Butter Cups.
5. Infectant Allergens
The allergy caused by the metabolic products of living microorganisms in the human body such as the continual presence of certain types of bacteria, protozoas, moulds, helminths, and other parasites. Which is present in chronic infection for which patients are not aware of.
Example of infectant allergens:
The continuous presence of growth products and metabolic wastes of parasitic organisms such as hookworms, tapeworms, tin worms, spread worms, and dermatophytes are referred to as infectant allergies.
- Thick, yellow/green discharge.
- Pain around cheeks and eyes.
Reference: Textbook of PharmaCognosy and PhytoChemistry by Biren Shah, A.K. Seth.