Infections[edit] => Allergic reaction to contact with specific chemicals, such as urushiol, derived from poison ivy or poison oak, or Balsam of Peru, found in many foods and fragrances.[7][8] Certain allergens may be diagnosed in a patch test.[9][10]&Body louse, found in substandard living conditions&Cutaneous larva migrans, a skin disease&Head lice, if limited to the neck and scalp&Herpes, a viral disease&Insect bites, such as those from mosquitos or chiggers&Photodermatitis – sunlight reacts with chemicals in the skin, leading to the formation of irritant metabolites&Pubic lice, if limited to the genital area&Scabies, especially when several other persons in close contact also itch&Shaving, which may irritate the skin&Swimmer's itch, a short-term immune reaction&Varicella – i.e. chickenpox, prevalent among young children and highly contagiou
Environmental and allergic[edit] => Foreign objects on the skin are the most common cause of non-pathological itching.&Urticaria (also called hives) usually causes itchin
Skin disorders[edit] => Dandruff – an unusually large amount of flaking is associated with this sensation&Punctate palmoplantar keratoderma, a group of disorders characterized by abnormal thickening of the palms and soles&Skin conditions (such as psoriasis, eczema, sunburn, athlete's foot, and hidradenitis suppurativa). Most are of an inflammatory nature.&Scab healing, scar growth, and the development or emergence of moles, pimples, and ingrown hairs from below the epidermis&Xerosis – dry skin, the most common cause,[citation needed] frequently seen in the winter and also associated with older age, frequent bathing in hot showers or baths, and high-temperature and low-humidity environment
Medical disorders[edit] => Diabetes mellitus, a group of metabolic diseases in which a person has high blood sugar&Hyperparathyroidism, overactivity of the parathyroid glands resulting in excess production of parathyroid hormone (PTH)[11]&Iron deficiency anemia, a common anemia (low red blood cell or hemoglobin levels)&Jaundice and cholestasis – bilirubin is a skin irritant at high concentrations&Malignancy or internal cancer, such as lymphoma or Hodgkin's disease[12]&Polycythemia, which can cause generalized itching due to increased histamines&Psychiatric disease ("psychogenic itch", as may be seen in delusional parasitosis)&Thyroid illness&Uraemia – the itching sensation this causes is known as uremic pruritu
Medication[edit] => Drugs (such as opioids) that activate histamine (H1) receptors or trigger histamine release&Chloroquine, a dru
Related to pregnancy[edit] => Gestational pemphigoid, a dermatosis of pregnancy&Intrahepatic cholestasis of pregnancy, a medical condition in which cholestasis occurs&Pruritic urticarial papules and plaques of pregnancy (PUPPP), a chronic hives-like ras
Other[edit] => Menopause, or changes in hormonal balances associated with agin
Pain and itch have very different 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 of scratching, as one would find noxious scratching highly pleasurable.[2] 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.[4] 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.[2]
Contagious itch[edit] => 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 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.[2]
Pain inhibition by itching[edit] => The sensation of itch can be reduced by many painful sensations. Studies done in the last decade have shown that itch can be inhibited by many other forms of painful stimuli, such as noxious heat,[5] physical rubbing/scratching, noxious chemicals, and electric shock.[6]