[0:03]Rhin refers to the nose and itis refers to inflammation, so rhinitis is nasal inflammation. Allergic rhinitis is also called hay fever, because it's typically caused by allergens like hay, as well as pollen, dust, animal hair or mold spores. Since 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. 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 the foreign particle and presents it to a nearby lymphocyte called a T cell. If that T cell gets activated, it kicks into action, producing cytokines, which help 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. 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 of 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. So those 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 grow 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. The symptoms of allergic rhinitis are related to excess fluid in the facial tissues. It causes nasal congestion and red, itchy, swollen eyes with frequent bouts of sneezing. Symptoms can start just minutes after exposure to allergens and can persist for weeks at a time, affecting the ability to concentrate and sleep, as well as attend work or school. The diagnosis of allergic rhinitis is generally based on simply the way the skin looks, and when possible, it's helpful to identify the allergic trigger so that a person can avoid them in the future. One way to identify an allergic trigger is with a skin prick test, where small drops of allergens are placed on the skin and then pricked into the skin with a tool. Again, this is to see if there's evidence of an allergy, like raised bumps or wheals, otherwise known as itchy red skin. These can test for a lot of allergens at once, but they can sometimes have low sensitivity as well as 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 an allergen in their everyday life, and that would be low specificity.
[3:59]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, which reduces 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 microdoses 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 the eyes and nose. 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 get inflamed and watery. Avoiding allergens is best, but also antihistamines and desensitization to reduce or eliminate the symptoms.
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