![]() ![]() The resulting reduction of sensation is associated with degeneration of epidermal nerve fibres, which is at least partially reversible ( Nagy 2004 Nolano 1999 Simone 1998). It is thought that degenerative changes in the primary sensory neuron result in loss of peripheral or central nociceptor-specific macromolecules and receptors, and that these degenerative changes can affect distant parts of the primary sensory neuron ( Jancso 2008). ![]() The mechanisms of desensitisation remain unclear. Enhanced sensitivity is followed by a refractory (unresponsive) period with reduced sensitivity and, after repeated applications, persistent desensitisation. There is an initial excitation of the neurons and a period of enhanced sensitivity to noxious stimuli, usually perceived as itching, pricking or burning sensations. It binds to nociceptors (sensory receptors responsible for sending signals that cause the perception of pain) in the skin, releasing proinflammatory neuropeptides, such as substance P, which cause neurogenic inflammation. In England in 2007 there were almost 149,000 prescriptions for topical capsaicin products ( PCA 2007).Ĭapsaicin is the active compound present in chilli peppers, responsible for making them hot when eaten. ![]() It is also available over the counter in some other countries. Capsaicin is available in the United Kingdom on prescription only but, according to the British National Formulary, may be present in small quantities in topical rubefacients (a substance for external application producing redness of the skin, or erythema) sold through pharmacies. Topical creams with capsaicin are used to treat pain from a wide range of chronic conditions including postherpetic neuralgia and diabetic neuropathy, osteoarthritis, and rheumatoid arthritis, in addition to pruritus, psoriasis, mastectomy pain, and cluster headaches ( Reynolds 1999). This compares with transdermal application, where the medication is applied externally and is taken up through the skin, but relies on systemic distribution for its effect. They exert their effects close to the site of application, and there is no substantial systemic uptake or distribution. Topical medications are applied externally and are taken up through the skin. ![]()
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