Allergic rhinitis

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Introduction0:00–0:27

“Rhin” refers to the nose and “itis” refers to inflammation, so rhinitis is nasal inflammation. Allergic rhinitis is also called hay fever, and it’s typically caused by allergens like hay, as well as pollen, dust, animal hair, or mold spores.
When the main trigger is pollinating plants, allergic rhinitis will flare up at specific times of the year. Allergic rhinitis is a type 1 hypersensitivity reaction, which is a type of allergic reaction that starts with exposure to an environmental allergen.

Physiology0:27–0:57

So - let’s say that a bit of pollen enters the nose. It can get picked up by a dendritic cell which is a type of immune cell that gobbles up foreign particles and presents it to a nearby lymphocyte called a T cell.
If the T cell gets activated, it kicks into action, producing cytokines which helps to get other immune cells involved. The exact type of T cell determines the type of immune response, and in allergic rhinitis there’s a bit of a T cell imbalance.

Pathology0:57–2:31

There are too many T cells that, when activated, stimulate B cells, another group of lymphocytes, to produce IgE antibodies.
Those IgE antibodies get released into the bloodstream and bind to mast cells, which are immune cells in the tissue that carry within themselves a load histamine.
Once bound by IgE the mast cells are “primed”, meaning if pollen enters the body again in the future, those mast cells degranulate and release their histamine into the local tissue.
The histamine causes blood capillaries to dilate and become leaky which brings more fluid and immune cells to the area where the mast cells are located.
Because the eyes and nose are portals of entry for infections, there are lots of mast cells around those areas for extra protection.
The IgE-primed mast cells release their histamine, which causes nearby capillaries to dilate - flooding the facial tissues with fluid.
Interestingly, there’s evidence that early exposure to allergens might protect against type 1 hypersensitivity. For example, children who grew up on farms and have pets at an early age typically have lower rates of allergic rhinitis.
It’s thought that a combination of genetic factors and environmental factors like these contribute to which type of T cell group is most common and thereby influences the overall immune response.

Symptoms2:31–2:57

The symptoms of allergic rhinitis are related to the excess fluid in the facial tissues. It causes nasal congestion, and red, itchy, swollen eyes with frequent bouts of sneezing.
Symptoms can begin just minutes after exposure to allergens, and can persist for weeks at a time, affecting the ability to concentrate and sleep, and to attend work or school.

Diagnosis2:57–3:55

The most common way to diagnose allergic rhinitis is through skin testing. One type is called the patch test, where allergens are applied to small patches and stuck onto the skin.
If the skin under a particular patch becomes irritated, it suggests an allergy to that substance. Another type is called scratch testing, and it’s when small drop of allergen are placed on the skin and then pricked into the skin with a tool; again, to see if there’s evidence of an allergy like raised bumps or weals - itchy red skin.
These tests can test for many allergens at once, but they can sometimes have low sensitivity and low specificity. In other words, sometimes a person might have no allergic reaction on the skin test, but have a localized allergic reaction affecting the nasal cavity and eyes - that’s low sensitivity.
Other times a person might have a skin reaction to something, even though they don’t normally have symptoms when they encounter that allergen in their everyday life - that’s low specificity.

Treatment3:55–4:37

Typically, the best thing for allergic rhinitis is to simply avoid the triggering allergen if possible. If there are symptoms, antihistamine medications can be used to suppress the effect of mast cell degranulation.
Nasal irrigation can flush out the sinuses, reducing the congestive symptoms of allergic rhinitis. In some situations, it’s also possible to rewire the body’s immune response to an allergen by exposing it to micro-doses and slowly ramping up to a full dose of the allergen.
This gradually boosts tolerance to the allergen by reducing the immune system’s tendency to produce IgE each time. Alright, as a quick recap - allergic rhinitis is a type 1 hypersensitivity reaction which results in inflammation of eyes and nose.

Review4:37–6:10

Airborne allergens like pollen, dust, animal hair, or mold spores cause mast cells in the tissues to release histamine, causing the eyes and nose to become inflamed and watery.
Avoiding allergens is the best approach, but it’s also possible to use antihistamines, and in severe cases try desensitization to reduce or eliminate the symptoms.
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