In allergic conditions, excess levels of histamine are secreted in response to harmless allergens over-stimulating the immune system. This causes allergy symptoms such as skin itching, inflammation, swelling, watery eyes and a runny nose.
The Effects of Histamine on the Tissues of the Body
Histamine is a compound released by the white blood cells that plays a key role in allergic reactions and the effects of allergies on various cells and tissues in the body. The chemical histamine is produced by white blood cells called eosinophils (mast cells) and basophils and signals to the immune system to respond to invading pathogens or foreign bodies.
In the lungs excess histamine can trigger allergy related asthma symptoms. Patients with allergy-induced asthma are more sensitive to higher levels of histamine, which causes bronchoconstriction or narrowing of the smooth muscles lining the bronchioles of the lungs. This also produces inflammation, spasms and mucus accumulation in the lungs. Symptoms of allergy induced asthma include coughing, wheezing, chest tightness and difficulty breathing.
Allergy Symptoms Caused by an Overactive Immune System
A runny nose is a common allergy symptoms and histamine is also the cause of this. High levels of histamine lead to angiodema or swelling in the mucous membranes lining the nose. This causes fluid to leak into the tissues causing itching, watery eyes, a runny nose, postnasal drip and sneezing.
Histamine has the same effect on the mucous membranes of the mouth, throat, lungs and gastrointestinal tract, causing swelling. In severe allergic reactions the swelling in the nose, mouth, throat and lungs can restrict and even obstruct breathing.
Histamine also increases production of thick mucous in the nasal passageways and lungs leading to a runny nose, nasal congestion and fluid in the lungs. This occurs in allergic reactions because both H1 and h2 receptors are activated producing excess mucous. Normally, these receptors are activated in an immune response to secrete mucous to capture foreign particles and germs in the body.
Histamine Effects on the Skin and Stomach
Excess secretion of histamine also causes the characteristic skin itching during an allergic reaction to an allergen that is eaten, touched or inhaled. This causes skin symptoms such as erythema or redness, swelling, inflammation, rashes, eczema and hives.
Histamine also an effect on the lining of the stomach, causing the gastric cells to increase production of acid secretions. For this reason, in some cases an allergic reaction may also cause stomach upset and increased acidity in the gastrointestinal tract.
References:
Mayo Clinic: Hives and Angiodema
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Noreen Kassem - Noreen Kassem is a hospital doctor based in London, UK. She has extensive experience in clinical research and an undergraduate honors ...
