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Physical urticaria
These types are very distinct and are induced by exogenous physical stimulus. The source of stimulus can be thermal, mechanical and cholinergic. Ten percent of chronic urticaria are physical urticaria. Considering the types of stimuli, these typs are categorized into sub-groups like dermatographism, delayed-pressure, cholinergic, cold, solar, heat, aquagenic and vibratory urticaria.Dermatographism is very common and induced by scratching or firmly stroking the skin. The swollen skin spots may appear immediately and resolve in about 30 minutes. In a normal healthy person though scratching may produce linear reddening without itching, in dermographism, itchy swelling develops. If the skin swelling persists or causes discomfort, taking antihistamines may resolve them.
Cholinergic or stress type is widespread and is caused due to rise in the core body temperature. Strenuous exercise and warm or hot bath may trigger the condition. Numerous small welts appear causing itching, tingling and burning sensation. The red spots appear quickly and last up to two hours. It is considered that psychosomatic influences stimulate parasympathetic nervous system leading to release of histamine throughout the body.
Cold influenced physical urticaria is common in youngsters. On exposure to cold winds, cold water and cold climate, red spots appear on exposed parts like face, neck and hands. There is another hereditary type which may cause red swollen spots all over the body, nine to eighteen hours after exposure. For persons with this condition, there is a grave danger in swimming in cold waters, as there may be massive release of histamine leading to low blood pressure and shock.
Delayed-pressure urticaria is a rare physical type and skin swelling occurs in the areas where there is sustained pressure. Usually in this delayed type, swollen spots appear approximately six hours from initial stimulus and may last between eight hours to three days. Belts, straps, tight-fitted clothing and activities giving sustained pressure on the skin can trigger this condition.
Heat induced urticaria is a rare physical type wherein swollen spots appear on continued application of heat. The spots may appear within two to three minutes of exposure and may last up to one hour.
Solar or sun induced urticaria is caused on exposure to sun on the exposed skin areas. Though this physical type appears within a few minutes of exposure, it resolves within a few hours from withdrawing the sun exposure. Depending upon the wavelength of light triggering the condition, six different types are known.
Water (aquagenic) urticaria is triggered on contact with water and the response is not temperature dependent. The skin swelling appears within one to ten minutes after the contact and may last up to two hours. Histamine release is not involved in this condition and there is a opinion that sensitivity of skin to additives in the water may the triggering factor.
Vibratory urticaria is a rare physical type and develops on contact with vibration. Painful angioedema develops within five minutes after contact with vibration and may last up to one hour.
Exercise-induced anaphylaxis is a rare physical type causing skin swelling and itchiness, shortage of breath and low blood pressure. The symptoms may appear within thirty minutes from the start of exercise and sometimes may prove fatal. Unlike cholinergic Urticaria, in this type hot bath does not trigger the condition. Hospitalization and treatment with antihistamines, epinephrine and ventilator support may be required.
Drug-induced type of urticaria
Many drugs have been found to cause allergic reactions like minor skin rashes and urticaria. The most common causes of drug induced allergy are penicillin and related antibiotics like amoxicillin and ampicillin. Other common urticaria inducing drugs are sulfonamides, antiepileptic drugs, antidiabetic drugs, insulin preparations, aspirin, dextroamphetamine and clotrimazole. Some of them can lead to severe physical symptoms like angioedema, severe asthma, anaphylaxis and cardio-respiratory failure.Knowing and avoiding the triggering factors and use of appropriate antihistamine medicines can resolve all types of physical urticaria without leaving any skin blemishes, discolorations and scars.
Related topic of interest:
Acute urticaria
Image:
James Heilman, MD, http://commons.wikimedia.org/wiki/User:Jmh649/CC BY-SA 3.0
References:
1.Marcus Maurer and Jürgen Grabbe, Urticaria: Its History-Based Diagnosis and Etiologically Oriented Treatment, Dtsch Arztebl Int. 2008 June; 105(25): 458–466. PMCID: PMC2696901
2.Barbaud A, [Physical urticaria], Ann Dermatol Venereol. 2003 May;130 Spec No 1:1S16-27, PMID: 12843805
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