Allergic to Dogs and Allergies in Dogs Resource

Allergens, Antigens and Allergies

What are Allergens?

In its simplest form, we can think of an allergen as:

“A substance that can cause an allergy”

A more complete definition would provide further information about the substance and the reason why an allergy occurs. Therefore, we could redefine an allergen as being:

“A normally harmless substance that triggers the immune system of an allergy sufferer resulting in an allergic reaction”

What are Antigens?

An antigen can be considered as a substance that the body perceives to be a threat and responds by producing an antibody to it. Antigens can be categorized as:

  • Exogenous Antigens – Antigens originating outside the body but entering the host through the skin or by being ingested or inhaled. This can include environmental substances, chemicals and microbes e.g. viruses, bacteria, fungi and parasites.
  • Endogenous Antigens – Antigens that are generated or formed within the body due to an infection.
  • Autoantigen or Autoimmune Disease – Failure of the body to recognize its own cells and tissue results in an immune response that is detrimental to the host.

What is the Difference Between an Allergen and Antigen?

Understanding the difference between the terms allergen and antigen can be confusing.

Allergens, Antigens and Allergies

The immune system responds to antigens by producing antibodies but not all antigens lead to an allergic reaction. Those antigens that trigger an allergic reaction are termed allergens or ‘allergen antigens’.

The production of antibodies – in particular IgE – to parasitic infections (microbial related antigens) is a common defensive mechanism. However, the immune response of producing IgE antibodies to a non-parasitic environmental allergen typically occurs only in individuals with a genetic tendency/hereditary predisposition (atopy) upon re-exposure to the allergen. Therefore, elevated IgE levels can be considered a marker of parasitic exposure (Cooper et al. 2008) and allergic disorders (Gould and Sutton 2008).

In general , most individuals with allergies are atopic. Allergy symptoms, such as allergic rhinitis or allergic asthma, are the result of IgE and various immune cells attempting to eliminate allergens from the body. However, not all allergy reactions involve the same underlying mechanism and this is discussed in the section concerning Antibodies (Immunoglobulins), Hypersensitivity and Allergies.

Furthermore, an allergen does not necessarily have to be a harmful substance in itself; it poses a risk only to those hypersensitive to it i.e. whose immune system is sensitized to it.  For example, dust mites, feathers or dog dander are not considered dangerous or poisonous per se but to an individual hypersensitive to them, they could trigger an allergic reaction that might be harmful to that individual. The severity of the allergy response resulting from exposure to an allergen will vary between individuals, and even then, it may not be the same from one day to the next.

Given that it is possible to be allergic to almost anything, some of the more common allergens include:
Dander, Drugs (Medication), Dust Mite Excretion, Feathers, Food, Mold, Pollen, Perfumes, Plants, Smoke.

Other things that may elicit an allergic reaction include:
Microbial-related (Bacteria, Fungi and possibly Viruses e.g. Gavala et al. 2013), chemicals and toxins.

How do Allergy Sufferers Come into Contact With Allergens?

Allergy sufferers come into contact with the allergens through:

  • Skin contact. This may include:
    • Direct skin contact. For example, through petting or being licked on the skin by a dog. Other examples include allergies to substances that people touch such as latex or insect stings.
    • Indirect skin contact. Allergen being transferred to the allergy sufferer through coming into contact (touching, shaking hands or contaminated clothing) with a person who’s had direct contact with the source of the allergen e.g. a dog.

The allergens can then enter the body:

    • Through the actual skin, or
    • By being transferred to the membranes in the mouth, nose or eyes e.g. by poking fingers into the mouth, picking one’s nose, rubbing eyes or even through kissing.

Allergens such as dander can become widely dispersed and result in problems for allergy sufferers in places where they would not expect to encounter them e.g. hotel rooms, public transport, offices, schools or homes without any resident pets. Also, unless filtration systems are both present and maintained properly (in ventilation, air conditioning and certain heating systems), allergens can be spread throughout an entire complex of offices or apartments. The onset of allergy symptoms without an obvious cause can be frustrating for both the individual who is unaware they suffer from a specific allergy, as well as those who have already been formally diagnosed.

Allergens can also enter the body via:

  • Ingestion of the allergen. This is obvious in the case of food allergies or those caused by taking medications orally, however, it can still be a mode of transmission when it comes to dog allergies. Letting a dog lick the fingers, hands, face or mouth of a person can lead to that individual consuming the dog allergens e.g. by inadvertently placing their fingers in their mouth some time later. In addition, it is possible for dog allergens to get into the food consumed by a person during the preparation process. In the case of a dog allergic to human dander, it can consume human allergens simply by licking a person; though rare, even passing a dog biscuit to a highly sensitive dog with a human allergy can trigger an allergic reaction in it!
  • Inhalation of air borne allergen particles, such as microscopic flakes of dander, entering the nose, sinuses, throat and lungs. This is probably the main mode of transmission for pet allergens. Furthermore, the most significant mammalian aeroallergens are from a family of proteins known as lipocalins.
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