Histamine is an important protein that's secreted by two types of white blood cells called eosinophils and basophils. It's involved in allergic reactions to substances that are normally not harmful to the body, such as pollen, dust, mold, animal fur, insect bites and certain foods. The release of histamine causes several allergic symptoms, such as the inflammatory response of the body, as explained by the Faculty of Cell Biology at Davidson College. In normal responses, histamine also has an essential role in the immune system to protect the body against invading pathogens or germs.
Asthma
The University of Maryland Medical Center says histamine plays a key role in allergy-induced asthma. When excess histamine is released into the blood by white blood cells, the immune system becomes oversensitive and attacks the lungs. This leads to irritation, inflammation, swelling and fluid buildup of the smooth muscle lining in the passageways of the lungs. Symptoms of asthma result, including difficulty breathing, wheezing, coughing and chest tightness and pain.
Nose and Throat Problems
Inhaled allergens can result in histamine producing a reaction in the tissue membranes that line the nasal passageways. This can cause several effects, including hay fever symptoms such as sneezing, watery eyes, a runny nose and nasal congestion. The fluid buildup in the nasal passageways can also lead to sinus congestion and infection-causing symptoms of pain and pressure in the facial and head area. The University of South Carolina Medical School explains that nasal congestion is an effect of increased histamine levels that dilate blood vessels in the mucous membrane that lines the nose, throat and sinuses. This causes fluid to leak from the blood vessels and into the nose, throat and sinuses.
Skin Effects
Allergic reactions are often most evident on this skin. In infants and children particularly, hives or red, raised itchy spots on the skin are commonly the first symptom of an allergy to a food or other substance. According to the Cleveland Clinic, skin irritation and itching may be localized and only affect the area that's exposed to the allergen, or it may be general and affect large areas of the body. In some cases, itching is a secondary effect of other allergy-related skin symptoms such as eczema and contact dermatitis. Increased levels of histamine circulating in the blood cause skin allergy reactions by triggering inflammation, irritation and swelling of the blood vessels in the skin layers. In most cases, skin symptoms such as hives and itching are temporary and treated effectively with an anti-histamine medication. Other allergy rashes such as eczema and contact dermatitis can last for several weeks or more.
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