Urticaria, also known as hives, is a skin allergic reaction with itchy wheals. Allergic reactions happen when your immune system comes in contact with an allergen. Allergens are proteins that are harmless to many people but cause an allergic reaction in sensitive people. The wheals often start as itchy patches that turn into swollen welts that vary in size. These wheals appear and fade at random as the condition runs its course.
Cause
Urticaria is a result of mast cells, a type of white blood cell being activated by your immune system such that histamine and inflammatory mediators are released to the affected area. This usually happens in response to certain external triggers. The histamine released by mast cells dilate blood vessels and increase capillary permeability, causing release of fluid into the skin. The buildup of fluid leads to swelling that occurs with urticaria and angioedema.
Mast cells can be activated commonly because of allergies. Allergic reaction occurs when a person’s immune system is sensitive to substances in the environment. Urticaria can also be caused by physical triggers such as mechanical stress, temperature changes, ultraviolet radiation, medications like aspirin, and some viral infection. Some patients of urticaria experience changes within their own body and not because of external agents. An overactive immune system or autoimmune diseases may trigger unwanted signals that activates muscle to release histamine.
All urticaria are acute initially. Some will become chronic urticaria after a period of time, usually defined as 6 weeks or more. Chronic urticaria can be caused by underlying medical conditions like thyroid disorders, hepatitis, and some forms of cancer.
Clinical features
Urticaria is a skin condition characterised by the transient appearance of wheals or hives on the skin, which are raised, red or pink, and itchy. They can appear on any area of the body, change shape, move around, disappear and reappear over short periods of time. The red or skin-coloured wheals with clear edges usually appear suddenly and go away just as quickly.
Blanching may occur when the centre of a red hive turns white under pressure.
Treatment
- First-line therapy
As an initial treatment for most patients, antihistamines could be prescribed to patients. Antihistamines block the action of histamine at the receptor, which is responsible for mediating the symptoms of allergic reactions, such as itching, redness, swelling, and wheals. It can reduce pruritus, flatten wheals, shorten wheal duration, and reduce wheal numbers, even though they may not clear urticaria completely. They are the mainstay of management for most patients with urticaria, and can be taken orally or topically, depending on the type and severity of the condition.
- Second-line therapy
For patients who have not responded well to antihistamine. They are usually prescribed with additive therapies (to antihistamines) rather than as alternatives.
Corticosteroids can be considered primarily for the short-term management of severe urticaria. They can reduce the inflammation and swelling associated with urticaria, and suppress the immune system’s response to allergens or other triggers that may cause urticaria.
Leukotriene receptor antagonists block the action of leukotrienes, lipid mediators that can contribute to inflammation and bronchoconstriction. They may be effective in some patients with chronic urticaria, especially those with associated asthma or aspirin sensitivity.
For non-drug approaches, patients may consider diet modifications. Excluding food additives and natural salicylates in diet which may potentially cause pseudoallergic reactions.
- Third-line therapy
To treat urticaria are typically reserved for patients with severe, refractory, or autoimmune forms of the disease, who have not responded to antihistamines and other treatments.
IVIg infusions are a type of treatment where a preparation of antibodies from healthy donors is given to patients. IVIg is used as a replacement therapy in patients with immunodeficiencies, who have low levels or defective function of IgG antibodies, or as an immunomodulatory therapy in patients with autoimmune or inflammatory diseases, who have excessive or aberrant immune responses.