What causes urticaria is more difficult to answer than what happens during urticaria, as we described on the earlier page. In almost half the cases we know what causes or induces urticaria; and half the time, the patients or we have no clue as to its exact causation.

It must be noted that Urticaria is not always allergic in nature. There are allergic and non-allergic causes for chronic urticaria. The non-allergic causes include auto-immunity related, stress triggered, exercise and temperature based and other factors. 

We shall try to examine some of the most common exciting factors known to induce urticaria, which may be grouped as:

Allergens:
A large number of allergens have been identified as causative agents for some cases of urticaria. It may be noted that urticaria is an individual hypersensitivity and the following factors may not cause urticaria in all urticaria-prone individuals.

Food allergens:
Milk, cheese, egg, protein products, wheat, cereals, certain daals as used in India, peas, orange, fish, chicken, etc. Synthetic and natural food additives and artificially-flavored food articles.

Urticaria and alcohol:
True anaphylactic reactions to alcohol (ethanol) are rare and most reactions to ingested alcoholic beverages are secondary to other chemicals in the beverage such as metabisulfite, papain, dyes or yeasts. However, there are reports of true allergic reactions in which the offending agent was shown to be the ethanol itself. Generally the symptoms of anaphylaxis occur in such patients following the ingestion of beer and/or wine. Urticarial rashes have been reported with ethanol ingestion; and hives on contact with ethanol have also been reported for some patients.

Environmental factors:
Exposure to pollen, house-dust, buffalo dander, fungi, change in temperature, etc. are known exciting factors. Extreme cold, heat, pressure may also induce urticaria.

Drugs:
The major cause for urticaria are man-made drugs such as antibiotics (Penicillin), anti-inflammatory drugs (aspirin, indomethacin), vaccinations, foreign sera, hormonal preparations, contraceptive pills, etc. Animals treated with penicillin excrete a small amount of it in the milk sufficient to cause urticaria in sensitive individuals.

Urticaria and cocaine:
There have been reports of morphine-induced hives in some people. Bronchospasm may occur in some patients who smoke cocaine or in those who inject heroin. This may occur more often in patients who have a previous history of asthma. Hypersensitivity pneumonitis to cocaine has also been described and is associated with elevated levels of IgE.

Infections and infestations:
Insect bites, Fungal, protozoal, frequent bacterial infections (Urinary tract), viral infections (Hepatitis), helminthiasis (worm infestations such as round worms, tapeworms), etc. are factors known to cause urticaria. Domestic contact with the pet animals should be examined as cause for urticaria.

Synthetic products:
Use of personal products such as deodorant, perfume, and talcum powder, cosmetic products, animal derivatives, and similar synthetic substances may induce this disorder.

Emotional factors:
Especially in chronic, recurring cases of urticaria the role of emotional factors must be examined. Emotional stresses may directly or indirectly make on susceptible to develop a tendency to urticaria. The psychological factors may work as exciting, aggravating or maintaining cause.

Autoimmune causes: Chronic urticaria is now understood to have autoimmune link. Presence of auto antibodies against Immunoglobulin E (IgE), CD23 (FcεRII or Fc epsilon RII) which releases histamine, hence leading to chronic urticaria.

Systemic and general disease:
Urticaria in some cases may present as a sign of other systemic or general internal disease such as hormonal disorders (hyperthyroidism), SLE, polycythaemia, reticuloses, etc. In certain variety of malignancies (cancer) urticaria may present as a precursor.

Idiopathic cause:
No list of causation is complete without adding a paragraph of 'Idiopathic' which simply implies causes which are unknown.