Antihistamine and histamine

Antihistamine – the most commonly used weapon against allergies and hay fever

If you are allergic the chances are quite high that your medicines contain antihistamine. This substance comes as both tablets, nasal spray and eye drops and is usually the medication that is first tried out in order to ease mild allergy problems of short duration. Antihistamine is also used in combination with other types of medicines to increase the effect. Antihistamine can be helpful against many types of allergies, such as hay fever, allergy to pets, dust mites, mould and certain foods.

Antihistamine tablets are found both over-the-counter in pharmacies and as prescription medicines. Both adults and children can use them. Even if antihistamine tablets are usually effective against allergies they may not ease all of your symptoms. In order for you to rid yourself of the problems you may need to use several different types of medicines, or a combined medicine where the antihistamine is one of the active substances. Don't give up if you are not immediately symptom free - ask your doctor to recommend something else if your current medicine is not helping you.

How does histamine and antihistamine work?

Histamine is a neurotransmitter naturally found in your body and is among other things affecting the immune system. When your body comes into contact with a substance it is not tolerating, for example pollen that swirls around in the air, getting stuck to the mucous membrane of your eyes and nose, histamine is released from mast cells, also referred to as "allergy cells", in the mucous membrane. Histamine causes the blood vessels to expand and the mucous membrane to swell. Your eyes as well as your nose will become runny and itchy. Histamine can also cause 'nettle rash' in the skin or airways to contract, which can lead to asthma symptoms.

Antihistamines block the effect of the histamine and thereby reduces the allergic reaction. Histamine is released early during the allergic reaction. The blocking of histamine using an antihistamine will quickly make you feel better - within an hour using tablets and within 15 minutes using nasal spray or eye drops.

Antihistamines - pros and cons

Sole use of an antihistamine tablet might be enough to alleviate mild allergy problems but if the early allergic symptoms are more severe it is often necessary to try something else. Antihistamines often show a good effect on a runny nose, sneezing, and itch of the nose while on a congested nose it is not as effective. Even if an antihistamine quickly soothes the allergy problems, it does not stop the inflammation of the mucous membrane. This is why it is common to combine antihistamine with corticosteroid, which reduces the actual inflammation. It is possible to do this by taking several different medicines (for example antihistamine tablets corticosteroid spray) or a nasal spray that contains a combination of antihistamine and corticosteroid spray. The benefit of this is that the medication is working on two fronts, ensuring a more rapid effect. 

Side effects of antihistamines

Antihistamines come with few side effects although older types of tablets may cause tiredness, drowsiness and headache. Nasal spray and eye drops with antihistamines may sometimes irritate the mucous membranes as the medicine is being taken, but otherwise side effects from modern antihistamine medicines are uncommon.If you are pregnant or breast feeding you should consult with your pharmacist or doctor beforehand. 

If you experience undesired effects and are not free of symptoms while using antihistamines and/or OTC corticosteroid sprays it is important that you speak with your doctor about other possible solutions. Everybody reacts differently to different medicines, and even though you might not recover from using one type of medicine, it is likely that you will be helped by another.

Histamine in food

Histamine is also found in certain foods and can cause food poisoning among people with allergies as well as non-allergic people. This is called histamine intolerance and is caused by an inability of the body to break down large amounts of histamine. Even though this can affect anyone, some people with allergies or asthma may be more sensitive to histamine in food than others.

Foods containing a lot of histamine are for example, wine, blue cheese, soured milk products, fish oil, mackerel, anchovy, tuna, soy sauce, ripened meat products and fermented vegetables. Generally you could say that the longer the food has been matured, the more histamine it contains. Often it is required that you eat more than one food containing a large amount of histamine in order for a reaction to be provoked. If that occurs you might experience symptoms such as nausea, vomiting, stomach pains, diarrhea, constipation, nettle rash, flush and headache. In a worst-case scenario this could lead to symptoms similar to those of an allergic shock, or anaphylaxis, but that is very unusual. If you are histamine intolerant you should avoid eating foods containing a lot of histamine.

UK/GEN/15/0057a               Date of preparation: December 2015  

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