The human body is an incredible machine. It has a self-repairing mechanism. If you think, only you are worried when some Injury, Inflammation or an Allergic reaction occurs. No!
Your body can cure you better. In response to Allergens or Injuries, the Immune System produces a chemical compound called Histamine. Histamine is present in all the tissues of the body. Histamine acts as a weapon to fight the external pathogens. Once released from the tissues, Histamine fights with the Allergens, following symptoms may be observed:

Running Nose
Sore Throat
Irritation
Cough
Sneezing

Why is Histamine important?
Histamine has various functions in the body. It plays a role in the Immune response, Digestion and Central Nervous System. It causes an immediate inflammatory response signaling your body of potential invaders. The blood vessels become wider enabling WBC's in traveling faster to the infected part. It lowers Blood Pressure and stimulates the secretion of Gastric acids in the stomach. It is involved in the breakdown of food in the stomach. Histamine is a Neurotransmitter that communicates chemical messages within the nerve cells. Histamine gathers in the synapses and keeps the body cells attached.
Histamine role in Injury
Mast cells of an injured tissue produce Histamine. The surrounding blood vessels dilate and increase permeability. The Leukocytes and plasma protein are able to reach the injured site. They fight infection and repair the injured tissues.
Histamine role in Allergic reaction
When the immune system finds some antigens the Mast cells produce Histamine. They produce Histamine in inordinate amounts. The release of the Histamine produces an allergic reaction in the body. The symptoms like watery eyes, swollen tissues, and runny nose may occur.

How to break Histamine in the Body
Histamine N-Methyltransferase ( HMT ) and Diamine Oxidase ( DAO ) are two enzymes involved in the breakup of Histamine. Histamine present in the Central Nervous System is broken down by Histamine N-Methyltransferase ( HMT ). Diamine Oxidase (DAO) causes the breakup of Histamine in the digestive tract. Among the two enzymes, DAO is regarded the major enzyme for breaking down the ingested Histamine.
Excess of Histamine causes
Histamine travels throughout the bloodstream. It produces serious effects on your Skin, Lungs, Brain and Cardiovascular System. Excess of Histamine may lead to Histamine Intolerance.
The Symptoms of Histamine intolerance are:
Hives
Itching
Nausea
Anxiety
Fatigue
Sneezing
Flushing
Dizziness
Hay Fever
Migraines
Headaches
Arrhythmia
Angioedema
Hypertension
Tissue swelling
Nasal congestion
Difficulty Breathing
Abdominal Cramps
Contact Dermatitis
Allergic Conjunctivitis
Abnormal Menstrual Cycle
Difficulty falling asleep

What causes high Histamine Levels in the Body
Histamine is produced in the Body. Deficiency of DAO may lead to Histamine Intolerance.
Certain foods contain Histamine naturally or medical conditions that block the production of DAO in the body may increase the levels of Histamine in the Body. These medical conditions are:
SIBO
Leaky Gut
DAO deficiency
Foods rich in Histamine
Gastrointestinal bleeding
Immediate Hypersensitivity Reactions

Causes of Low DAO
Following may cause low levels of DAO in the body:
Celiac Disease
Genetic Mutations
Ulcerative Colitis
Leaky Gut Syndrome
Inflammatory Bowel Disease
Inflammation from Crohn’s Disease
Medications like Aspirin and Ibuprofen
Small Intestinal Bacterial Overgrowth ( SIBO )
Histamine Blockers like Pepcid, Tagamet, Zantac
Immune Modulators such as Enbrel, Humira, Plaquenil
Antidepressants like Prozac, Cymbalta, Zoloft, Effexor
Antiarrhythmics like Norvasc, Cardizem, Propanolol, Metaprolol,
Tea, Alcohol and Energy drinks block the production of DAO

Foods rich in Histamine:
Figs
Beer
Wine
Kefir
Dates
Olives
Yogurt
Pickles
Prunes
Raisins
Vinegar
Apricots
Spinach
Walnuts
Peanuts
Eggplant
Sour milk
Cashews
Avocados
Soy sauce
Kombucha
Tomatoes
Buttermilk
Sour cream
Champagne
Mayonnaise
Citrus fruits

Reducing the effects of Histamine
Antihistamines are used for reducing or getting rid of the Histamine effects. These are:
Basil
Papaya
Fennel
Ginger
Thyme
Vitamin C
Echinacea
Chamomile
Jewelweed
Wild Oregano
Stinging Nettle
Reishi Mushroom

Complete list of Antihistamines is available under the Actions section.