Itching is the biggest problem for patients with urticaria. Especially night itching can be extremely stressful, because it disturbs sleep, and it represents a dramatic restriction of quality of life.
Itching is particularly severe for patients who suffer from so-called urticaria factitia. Here scratching and rubbing the skin leads to the appearance of new hives and to further itching. The slightest irritation of the skin, e.g. unconscious rubbing of the skin during sleep can cause severe attacks of itching.
Emergence of itching
The release of histamine from mast cells leads directly to itching.
Many substances can trigger itching. The common feature of these substances is that they release the neurotransmitter histamine into the tissue, which plays a key role in triggering itching. The so-called mast cells of the immune system release certain neurotransmitters (particularly histamine). Almost all of the histamine that occurs in the skin is stored in the so-called mast cells. If these cells are activated, i.e. these cells are triggered by a stimulus, then this is the starting signal for a localized or diffuse spreading inflammation of the skin. As a result, the capillaries widen, the skin swells and becomes red and itchy, and wheals form.
However, histamine also stimulates nerve fibers in the skin, which then release certain itch-inducing substances (neuropeptides). These neuropeptides not only cause itching but in turn activate mast cells, so that a vicious circle begins, ending only when no further mast cells and nerves can be activated. Mast cells are predominantly located in the immediate vicinity of blood vessels and nerves. Therefore, the communication between mast cells, vascular cells, and nerve fiber is excellent.
After an insect bite or after contact with nettles, we feel the itch-inducing effect of histamine most strongly. In addition to substances that release endogenous histamine, the venom of many insects and also the poisons produced by itch-inducing plants contain histamine, which penetrates the skin and irritates it. This stimulus causes us to scrape or rub the skin and allows more blood to get to this point, so the irritants can be removed faster.