Urticaria: etiology and classification

Basic classification of urticaria

Urticaria is not a single disease—it is a group of nosologies united by a common clinical pattern. The key criterion for differentiating the forms is the time factor (duration of symptom persistence):

• Acute form: clinical manifestations persist for no more than 6 weeks. In this case, the etiological search is usually successful (the patient links the rash to food, medications, or insect bites).
• Chronic form: urticarial rashes recur or persist continuously for over 6 weeks. Identifying the root cause is significantly more difficult in this form (achieved in only 21–55% of cases).

Depending on the exposure to triggers, the following types are distinguished:

1. Spontaneous: occurs without any apparent external influence. About 40% of cases of chronic spontaneous urticaria (CSU) have an autoimmune origin. In such patients, the levels of total and specific IgE are often elevated, though this does not always indicate a true allergy.
2. Induced (physical): triggered by specific physical stimuli, including physical exertion.
3. Specific types:
4. Aquagenic — reaction to water (extremely rare in children).
5. Contact — occurs upon contact with chemical substances or proteins (e.g., latex). Carries a high risk of progression to systemic anaphylaxis.
6. Cholinergic — triggered by an increase in body temperature.

In pediatrics (where the condition is generally recorded less frequently than in adults—in 3.4–5.4% of children), special attention is paid to secondary urticaria. It is associated with underlying conditions: infections, cryoglobulinemia, and autoimmune processes.

The role of dietary factors and allergy

During acute episodes, patients often link the rash to recent food intake. Typical triggers include: cow's milk proteins, chicken eggs, peanuts, soy, wheat, tree nuts, and seafood.

However, true food allergy is rarely confirmed. Its verification requires the coincidence of three factors:

• A clear history of rash linked to exposure;
• Detection of specific immunoglobulin E (IgE) antibodies in the blood;
• Positive results from provocation tests.

In addition to classic allergens, exacerbations can be triggered by food additives (dyes, preservatives) and foods with high natural salicylate content: tomatoes, apricots, oranges, plums, raspberries, cherries, and currants.

Pseudoallergy: histamine metabolism disorders

Frequently recurring rashes are caused not by an immune system malfunction, but by the body's high sensitivity to the main inflammatory mediator—histamine. The accumulation of this substance occurs via two main pathways:

• Exogenous (alimentary): intake of histamine or its precursor (histidine) from the outside. A classic example is the consumption of fish nearing its expiration date.
• Endogenous (enzymopathic): impaired breakdown of histamine inside the body due to a deficiency or reduced activity of the enzyme diamine oxidase (DAO).

Drug and infectious triggers

Medications can provoke rashes, including through iatrogenic inhibition of the DAO enzyme. The list of potentially hazardous drugs includes:

• Antibiotics and antimicrobial agents: penicillins, cephalosporins, carbapenems (imipenem), isoniazid, pentamidine;
• NSAIDs (nonsteroidal anti-inflammatory drugs);
• Cardiovascular medications: verapamil, dobutamine;
• Mucolytics: acetylcysteine.

In addition to medications, infections can act as triggers. A link between the disease and hepatitis B virus (HBV) has been proven, and the role of Helicobacter pylori and odontogenic infection foci is being discussed. Parasites play a huge role: protozoa (Giardia lamblia, Blastocystis hominis), ectoparasites (bedbugs), and a wide range of helminths (toxocara, echinococci, ascarids, and others).

Class and exam questions

What else to study on this topic

• Pathogenesis of the urticarial wheal formation
• Diagnostic criteria and mechanisms of angioedema development
• Role and functions of the diamine oxidase (DAO) enzyme
• Clinical picture of specific types of induced urticaria
• Algorithm for performing provocative allergological tests

Other topics in "Chapter 5. Allergic Diseases"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.