A rash is a change of the skin that affects its color, appearance, or texture.
33-521: A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch , become warm, bumpy, chapped , dry, cracked or blistered , swell, and may be painful. The causes, and therefore treatments for rashes, vary widely. Diagnosis must take into account such things as the appearance of the rash, other symptoms, what the patient may have been exposed to, occupation, and occurrence in family members. The diagnosis may confirm any number of conditions. The presence of
66-399: A flare reaction that involves no histamine. Therefore, it is possible that pruritoceptive nerve fibres have different classes of fibres, which is unclear in current research. Histology and skin layers . Studies have 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 verified
99-442: A withdrawal reflex , whereas itches leads to a scratch reflex . Unmyelinated nerve fibers for itches and pain both originate in the skin . Information for them is conveyed centrally in two distinct systems that both use the same nerve bundle and spinothalamic tract . Most commonly, an itch is felt in one place. If it is felt all over the body, then it is called generalized itch or generalized pruritus . Generalized itch
132-515: A complete 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. Gene expression . Using single-cell mRNA sequencing, clusters of genes expressed in itch-related tissues were identified, e.g. NP1-3, transmitting itch information; where NP3 expresses neuropeptides Nppb and Sst as well as genes involved in inflammatory itch ( Il31ra , Osmr and Crystrl2 ). The histamine receptor gene Hrh1
165-430: 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 chronic inflammation . NGF
198-465: A patient has been diagnosed with. Common rashes can be easily remedied using steroid topical creams (such as hydrocortisone ) or non-steroidal treatments. Many of the medications are available over the counter in the United States. The problem with steroid topical creams i.e. hydrocortisone; is their inability to penetrate the skin through absorption and therefore not be effective in clearing up
231-456: 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 one imitates certain motor actions when they view others performing the same action. A similar hypothesis has been used to explain
264-402: A rash extremely difficult. An accurate evaluation by a provider may only be made in the context of a thorough history, i.e. medications the patient is taking, the patient's occupation, where the patient has been and complete physical examination. Points typically noted in the examination include: A patch test may be ordered, for diagnostic purposes. Treatment differs according to which rash
297-414: A rash may aid diagnosis; associated signs and symptoms are diagnostic of certain diseases. For example, the rash in measles is an erythematous , morbilliform , maculopapular rash that begins a few days after the fever starts. It classically starts at the head, and spreads downwards. Common causes of rashes include: Uncommon causes: The causes of a rash are numerous, which may make the evaluation of
330-439: 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. A variety of over-the-counter and prescription anti-itch drugs are available. Some plant products have been found to be effective anti-pruritics, others not. Non-chemical remedies include cooling, warming, soft stimulation. Topical antipruritics in
363-482: A way to relieve oneself by reducing the annoying itch sensation. However, there are hedonic aspects to scratching, as one would find 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
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#1732772302185396-466: 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
429-413: Is changed either very little or not at all by medical isolation of ill persons or medical quarantine for exposed persons. Thus, a "contagious disease" is sometimes defined in practical terms, as a disease for which isolation or quarantine are useful public health responses. Some locations are better suited for the research into the contagious pathogens due to the reduced risk of transmission afforded by
462-653: Is evenly distributed across the skin and has a clear spot distribution with similar density to that of pain. The different substances that elicit itch upon intracutaneous injection (injection within the skin) elicit only pain when injected subcutaneously (beneath the skin). Itch is often classified as that which is histamine mediated (histaminergic) and nonhistaminergic. Itch is readily abolished in skin areas treated with nociceptor excitotoxin capsaicin but remains unchanged in skin areas rendered touch insensitive by pretreatment with anti-inflammatory saponins . Although experimentally induced itch can still be perceived under
495-477: Is infrequently a symptom of a serious underlying condition, such as cholestatic liver disease. If the sensation of itching persists for six weeks or longer, then it is called chronic itch or chronic pruritus . Chronic idiopathic pruritus or Chronic Pruritus of Unknown Origin is a form of itch that persists for longer than six weeks, and for which no clear cause can be identified . Pain and itch have very different behavioral response patterns. Pain elicits
528-530: Is itch induced centrally but with no neural damage, is mostly associated with increased accumulation of exogenous opioids and possibly synthetic opioids. 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). Inflammatory mediators—such as bradykinin , serotonin (5-HT) and prostaglandins —released during
561-443: Is known to up-regulate neuropeptides, especially substance P . Substance P has been found to have an important 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 many granules rich in histamine, during long-term interaction. Noxious input to
594-449: Is often known to be contagious before medical science discovers its causative agent . Koch's postulates , which were published at the end of the 19th century, were the standard for the next 100 years or more, especially with diseases caused by bacteria . Microbial pathogenesis attempts to account for diseases caused by a virus . Originally, the term referred to a contagion or disease transmissible only by direct physical contact. In
627-445: 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
660-480: Is thought to alleviate itch by acting on the IL-4 receptor on sensory neurons. The effectiveness of therapeutic options for people who are terminally ill with malignant cancer is not known. Approximately 280 million people globally, 4% of the population, have difficulty with itchiness. This is comparable to the 2–3% of the population who have psoriasis . In 1660, German physician Samuel Hafenreffer introduced
693-410: 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
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#1732772302185726-536: The GRP neurons activate GRPR neurons to promote itch 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 . Neurogenic itch, which
759-492: The affected area, thus rendering the hydrocortisone almost completely ineffective in all except the most mild of cases. Itch An itch (also known as pruritus ) is a sensation that causes a strong desire or reflex to scratch . Itches have resisted many attempts to be classified as any one type of sensory experience. Itches have many similarities to pain , and while both are unpleasant sensory experiences, their behavioral response patterns are different. Pain creates
792-439: The cause of contagious yawning . Studies done in the last decade have shown that itch can be inhibited by many other forms of painful stimuli, such as noxious heat, physical rubbing/scratching, noxious chemicals, and electric shock . Itch can originate in the peripheral nervous system ( dermal or neuropathic ) or in the central nervous system (neuropathic, neurogenic , or psychogenic ). Itch originating in
825-623: The definition of pruritus (itch). Contagious disease A contagious disease is an infectious disease that can be spread rapidly in several ways, including direct contact, indirect contact, and Droplet contact . These diseases are caused by organisms such as parasites, Bacteria , Fungi , and viruses . While many types of organisms live on the human body and are usually harmless, these organisms can sometimes cause disease. Some common infectious diseases are Influenza , COVID-19 , Ebola , hepatitis , HIV/AIDS , Human papillomavirus infection , Polio , and Zika virus . A disease
858-453: The depth by injecting individual itch powder ( Mucuna pruriens ) spicules and noting that maximal sensitivity occurred 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
891-678: The existence of devices such as the back scratcher . Often, however, scratching only offers temporary relief and can intensify itching, even causing further damage to the skin, dubbed the "itch-scratch cycle". The mainstay of therapy for dry skin is maintaining adequate skin moisture and topical emollients . No studies have been conducted to investigate the effectiveness of emollient creams, cooling lotions, topical corticosteroids, topical antidepressants, systemic antihistamines, systemic antidepressants, systemic anticonvulsants, and phototherapy on chronic pruritus of unknown origin. However, there are clinical trials currently underway with dupilumab which
924-405: The form of creams and sprays are often available over-the-counter . Oral anti-itch drugs also exist and are usually prescription drugs . The active ingredients usually belong to the following classes: Phototherapy is helpful for severe itching, especially if caused by chronic kidney disease . The common type of light used is UVB . Sometimes scratching relieves isolated itches, hence
957-462: 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 very 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 place one scratches. Results from a study showed that itching and scratching were induced purely by visual stimuli in
990-505: The modern-day, the term has sometimes been broadened to encompass any communicable or infectious disease. Often the word can only be understood in context, where it is used to emphasize very infectious , easily transmitted, or especially severe communicable diseases. In 1849, John Snow first proposed that cholera was a contagious disease. Most epidemics are caused by contagious diseases, with occasional exceptions, such as yellow fever . The spread of non-contagious communicable diseases
1023-422: The pruriceptive primary afferent has been activated, the signal is transmitted from the skin into the spinal dorsal horn. In this area, a number of interneurons will either be inhibited or activated to promote activation of projection neurons, mediating the pruriceptive signal to the brain. The GRP-GRPR interneuron system has been found to be important for mediating both histaminergic and non-histaminergic itch, where
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1056-658: The skin is known as pruritoceptive , and can be induced by a variety of stimuli, including mechanical, chemical, thermal, and electrical stimulation, or infection. The primary afferent neurons responsible for histamine -induced itch are unmyelinated C-fibres . Nociceptors . Two major classes of human C-fibre nociceptors exist: mechano-responsive nociceptors and mechano-insensitive nociceptors. Mechano-responsive nociceptors have been shown in studies to respond to mostly pain, and mechano-insensitive receptors respond mostly to itch induced by histamine. However, it does not explain mechanically induced itch or itch produced without
1089-748: Was found in NP2 and NP3, suggesting that histaminergic itch is transmitted by both these pruriceptive sub clusters. Infection . Staphylococcus aureus , a bacterial pathogen associated with itchy skin diseases, directly activates pruriceptor sensory neurons to drive itch. Skin exposure to S. aureus causes robust itch and scratch-induced damage. This reaction is mediated by S. aureus serine protease V8 which cleaves proteinase-activated receptor 1 ( PAR1 ) on mouse and human sensory neurons. Targeting PAR1 through genetic deficiency, small interfering RNA ( siRNA ) knockdown, or pharmacological blockade decreases itch and skin damage caused by V8 and S. aureus exposure. After
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