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why does heat make my skin itch

An itch, besides being an irresistible sensation, is one of the main symptoms of an inflammatory skin disease. Yet scratching only makes the problem worse. Warm weather doesn't help either it is well known that heat exacerbates itching, however, little is known about the underlying biology. Now, a team of researchers led by dermatologist Hiroyuki Murota of Osaka University in Japan, and including dermatologist Mustafa Abd El-Latif at Cairo University, has determined the mechanism by which heat worsens an itch. First, they treated fibroblasts, or connective tissue cells, in culture with various chemicals linked to itching and pain, and measured gene expression in the cells.

The neuropeptide substance P caused the cells to express a growth factor called artemin. Next, the team examined sections of skin taken from patients with atopic dermatitis, a chronic skin condition characterised by scaly and itchy rashes. This revealed that artemin-expressing fibroblasts accumulate in the lesions. They then injected artemin or substance P into the skin of healthy mice and found that both induced branching of itch-sensing nerve fibres under the surface of skin, causing the mice to become hypersensitive to warm temperatures. This suggested to the researchers that artemin is somehow involved in temperature-dependent hypersensitivity.

To confirm these findings, they performed behavioural tests on mutant mice lacking the artemin receptor, and found that heat doesn't make the itch worse. "We are now investigating how artemin sensitizes the nervous system and leads to thermal hyperalgesia," says Murota. "We believe that this might provide some idea to develop novel therapeutic strategies. Topical artemin-neutralization might be one of the treatment strategies to attenuate warmth-provoked itch. "
doi:10. 1038/nmiddleeast. 2012. 155 The appearance of the heat rash depends upon where the excess sweat is deposited in the skin.

Tiny that look like small beads of sweat are seen if the sweat is blocked at the most superficial layers of the skin where the sweat duct opens on the skin surface. Called miliaria crystallina, it has no symptoms other than these sweat bubbles. Classic heat rash or miliaria rubra occurs if the sweat causes inflammation in the deeper layers of the epidermis. Like any other inflammation, the area becomes red (and therefore the name rubra = red) and the blisters become slightly larger. Because the sweat ducts are blocked and don t deliver sweat to the skin s surface, the area involved is dry and can be irritated, itchy, and sore.

This rash is also called prickly heat. Less commonly, after repeated episodes of prickly heat, the heat rash may inflame the deeper layer of the skin called the dermis, and cause miliaria profunda. This rash is made up of larger, harder bumps that are more skin colored. The rash begins almost immediately after, and again no sweat can be found on the affected areas. Rarely, this type of heat rash may be potentially dangerous if enough skin is involved, since the lack of sweating can lead to heat-related illnesses like, or.

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