What to do for itchy skin due to allergies
Itch can originate in the peripheral nervous system (dermal or neuropathic) or in the central nervous system (neuropathic, neurogenic, or psychogenic). When there is no identifiable cause it is known as essential pruritus.
Neuropathic itch can originate at any point along the afferent pathway as a result of damage of the nervous system. They could include diseases or disorders in the central nervous system or peripheral nervous system. Examples of neuropathic itch in origin are notalgia paresthetica, brachioradial pruritus, brain tumors, multiple sclerosis, peripheral neuropathy, and nerve irritation.
Inflammatory mediators—such as bradykinin, serotonin (5-HT) and prostaglandins—released during a painful or pruritic inflammatory condition not only activate pruriceptors but also cause acute sensitization of the nociceptors.
In addition, expression of neuro growth factors (NGF) can cause structural changes in nociceptors, such as sprouting. NGF is high in injured or inflamed tissue. Increased NGF is also found in atopic dermatitis, a hereditary and non-contagious skin disease with chronicinflammation. NGF is known to up-regulate neuropeptides, especially substance P. Substance P has been found to own an significant role in inducing pain; however, there is no confirmation that substance P directly causes acute sensitization.
Instead, substance P may contribute to itch by increasing neuronal sensitization and may affect release of mast cells, which contain numerous granules wealthy in histamine, during long-term interaction.
Itch originating in the skin is known as pruritoceptive, and can be induced by a variety of stimuli, including mechanical, chemical, thermal, and electrical stimulation. The primary afferent neurons responsible for histamine-induced itch are unmyelinatedC-fibres.
Two major classes of human C-fibrenociceptors exist: mechano-responsive nociceptors and mechano-insensitive nociceptors.
Mechano-responsive nociceptors own been shown in studies to reply to mostly pain, and mechano-insensitive receptors reply mostly to itch induced by histamine. However, it does not explain mechanically induced itch or when itch is produced without a flare reaction which involves no histamine. Therefore, it is possible that pruritoceptive nerve fibres own diverse classes of fibres, which is unclear in current research.
Studies own been done to show that itch receptors are found only on the top two skin layers, the epidermis and the epidermal/dermal transition layers. Shelley and Arthur had verified the depth by injecting individual itch powder spicules (Mucuna pruriens), and found that maximal sensitivity was found at the basal cell layer or the innermost layer of the epidermis.
Surgical removal of those skin layers removed the ability for a patient to perceive itch. Itch is never felt in muscle or joints, which strongly suggests that deep tissue probably does not contain itch signaling apparatuses.
Sensitivity to pruritic stimuli is evenly distributed across the skin, and has a clear spot distribution with similar density to that of pain. The diverse substances that elicit itch upon intracutaneous injection (injection within the skin) elicit only pain when injected subcutaneously (beneath the skin).
Itch is readily abolished in skin areas treated with nociceptor excitotoxincapsaicin, but remains unchanged in skin areas which were rendered touch-insensitive by pretreatment with saponins, an anti-inflammatory agent.
Although experimentally induced itch can still be perceived under a finish A-fiber conduction block, it is significantly diminished. Overall, itch sensation is mediated by A-delta and C nociceptors located in the uppermost layer of the skin.
Itch is also associated with some symptoms of psychiatric disorders such as tactile hallucinations, delusions of parasitosis, or obsessive-compulsive disorders (as in OCD-related neurotic scratching).
Neurogenic itch, which is itch induced centrally but with no neural damage, is mostly associated with increased accumulation of exogenous opioids and possibly synthetic opioids.
Noxious input to the spinal cord is known to produce central sensitization, which consists of allodynia, exaggeration of pain, and punctuate hyperalgesia, extreme sensitivity to pain.
Two types of mechanical hyperalgesia can occur: 1) touch that is normally painless in the uninjured surroundings of a cut or tear can trigger painful sensations (touch-evoked hyperalgesia), and 2) a slightly painful pin prick stimulation is perceived as more painful around a focused area of inflammation (punctuate hyperalgesia). Touch-evoked hyperalgesia requires continuous firing of primary afferent nociceptors, and punctuate hyperalgesia does not require continuous firing which means it can persist for hours after a trauma and can be stronger than normally experienced. In addition, it was found that patients with neuropathic pain, histamine ionophoresis resulted in a sensation of burning pain rather than itch, which would be induced in normal healthy patients.
This shows that there is spinal hypersensitivity to C-fiber input in chronic pain.
Signs and symptoms
Pain and itch own extremely diverse behavioral response patterns. Pain evokes a withdrawal reflex, which leads to retraction and therefore a reaction trying to protect an endangered part of the body. Itch in contrast creates a scratch reflex, which draws one to the affected skin site. Itch generates stimulus of a foreign object underneath or upon the skin and also the urge to remove it. For example, responding to a local itch sensation is an effective way to remove insects from one’s skin.
Scratching has traditionally been regarded as a way to relieve oneself by reducing the annoying itch sensation. However, there are hedonic aspects to scratching, as one would discover noxious scratching highly pleasurable. This can be problematic with chronic itch patients, such as ones with atopic dermatitis, who may scratch affected spots until they no longer produce a pleasant or painful sensation, instead of when the itch sensation disappears. It has been hypothesized that motivational aspects of scratching include the frontal brain areas of reward and decision making.
These aspects might therefore contribute to the compulsive nature of itch and scratching.
Events of «contagious itch» are extremely common occurrences.
Even a discussion on the topic of itch can give one the desire to scratch. Itch is likely to be more than a localized phenomenon in the put we scratch.
Results from a study showed that itching and scratching were induced purely by visual stimuli in a public lecture on itching. The sensation of pain can also be induced in a similar fashion, often by listening to a description of an injury, or viewing an injury itself.
There is little detailed data on central activation for contagious itching, but it is hypothesized that a human mirror neuron system exists in which we imitate certain motor actions when we view others performing the same action.
A similar phenomenon in which mirror neurons are used to explain the cause is contagious yawning.
Itch inhibition due to pain
The sensation of itch can be reduced by numerous painful sensations.
Studies done in the final decade own shown that itch can be inhibited by numerous other forms of painful stimuli, such as noxious heat, physical rubbing/scratching, noxious chemicals, and electric shock.
In 1660, German physician Samuel Hafenreffer defined itch.
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Approximately 280 million people globally, 4% of the population, own difficulty with itchiness. This is comparable to the 2–3% of the population suffering from psoriasis.
- Herpes, a viral disease
- Shaving, which may irritate the skin
- Head lice, if limited to the neck and scalp
- Swimmer’s itch, a short-term immune reaction
- Insect bites, such as those from mosquitos or chiggers
- Pubic lice, if limited to the genital area
- Cutaneous larva migrans, a skin disease
- Body louse, found in substandard living conditions
- Varicella – i.e. chickenpox, prevalent among young children and highly contagious
- Scabies, especially when several other persons in shut contact also itch
- Tungiasis, ectoparasite of skin
- Drugs (such as opioids) that activate histamine (H1) receptors or trigger histamine release
- Chloroquine, a drug used in the treatment and prevention of malaria
- Punctate palmoplantar keratoderma, a group of disorders characterized by abnormal thickening of the palms and soles
- Scab healing, scar growth, and the development or emergence of moles, pimples, and ingrown hairs from under the epidermis
- Dandruff – an unusually large quantity of flaking is associated with this sensation
- Skin conditions (such as psoriasis, eczema, seborrhoeic dermatitis, sunburn, athlete’s foot, and hidradenitis suppurativa).
Most are of an inflammatory nature.
- Xerosis – dry skin, the most common cause, frequently seen in the winter and also associated with older age, frequent bathing in boiling showers or baths, and high-temperature and low-humidity environments
- Menopause, or changes in hormonal balances associated with aging
Main article: Antipruritic
A variety of over-the-counter and prescription anti-itch drugs are available.
Some plant products own been found to be effective anti-pruritics, others not. Non-chemical remedies include cooling, warming, soft stimulation.
Topical antipruritics in the form of creams and sprays are often available over-the-counter.
Oral anti-itch drugs also exist and are generally prescription drugs. The athletic ingredients generally belong to the following classes:
Phototherapy is helpful for severe itching, especially if caused by kidney failure. The common type of light used is UVB.
Sometimes scratching relieves isolated itches, hence the existence of devices such as the back scratcher. Often, however, scratching can intensify itching and even cause further damage to the skin, dubbed the «itch-scratch-itch cycle.»
The mainstay of therapy for dry skin is maintaining adequate skin moisture and topical emollients.