When your body's immune system senses an allergen or a foreign tissue, part of its response is to produce histamine. Histamine brings blood and lymph fluid to the area that is under "attack" by an allergen. The blood and lymph fluid, in turn, attract immune cells in an attempt to free your body of this allergen. A person who is sensitive to certain allergens will experience typical allergy symptoms such as coughing, sneezing, hives, or a runny nose and tears as histamine is produced in their body. An extreme overreaction will cause a much more serious condition called anaphylactic shock, which can result in death if not treated immediately.
Too Much Histamine
Histamine production not only causes runny eyes and a stuffy nose, but histamines can also produce hives in reaction to cold, or when exposed to animal hair or another irritant. Most mild allergy attacks will either resolve themselves spontaneously or with the help of an antihistamine. However, some people have an immune system that is so reactive that their body experiences a severe allergy attack leading to anaphylaxis. If you have experienced a severe allergy attack in the past, to a bee sting, food or some other allergen, advise your doctor. She will be able to explain what steps you need to take if you ever experience anaphylaxis. Allergy-induced anaphylaxis makes your throat swell up until it closes, and needs to be treated immediately. You will be advised to wear a medic alert bracelet or necklace, as well as to carry medications that will work quickly to alleviate the symptoms. Teach your friends and relatives what they need to do to help you if you experience anaphylaxis as a result of a severe allergy reaction. Learn what triggers your allergies and avoid these triggers as much as you can.
Antihistamine medicines, which can be over the counter or prescription strength, block the histamines your body produces in reaction to allergens or other triggers. Oral antihistamines tend to cause sleepiness, since histamine found in brain cells are necessary for waking. If you block histamine production, you will subsequently feel drowsy and should not drive or operate machinery. This side effect is more common in older antihistamines that contain diphenhydramine or chlorpheniramine. Antihistamine nasal spray or eye drops can alleviate stuffy nose and sinus congestion, or redness and swelling in your eyes. Antihistamine medications only last for a few hours and need to be taken regularly during exposure to an allergen or when experiencing other symptoms, such as hives. They provide relief from the symptoms that too much histamine in your body creates.