Internet addiction disorder, more commonly called problematic Internet use (PIU), refers to excessive Internet use that interferes with daily life.

Internet addiction disorder is not listed in the latest DSM manual (DSM-5, 2013), which is commonly used by psychiatrists. Gambling disorder is the only behavioural (non-substance related) addiction included in DSM-5. However Internet gaming disorder is listed in Section III, Conditions for Further Study, as a disorder requiring further study.

Jerald J. Block, M.D. has argued that Internet addiction should be included as a disorder in the DSM-5. However, Block observed that diagnosis was complicated because 86% of study subjects showing symptoms also exhibited other diagnosable mental health disorders.

Acute urticaria (short-term): can develop suddenly and will last "less" than 6 weeks. About 1 in 6 people will have acute hives at one point in their life.

Chronic urticaria (long-term): can develop suddenly and will persist "more" than 6 weeks. This type of urticaria is uncommon and occurs in only 0.1% of the population. 20% of people with chronic urticaria report still having problems 10 years after its onset.

Characterized by dermal edema (wheal) and erthema (flare) also known as hives. Hive lesions typically last less than 24 and are usually pruritic. Hives can appear on anywhere on the body and they may change shape, move around, disappear and reappear over short periods of time.

Food intolerance is more chronic, less acute, less obvious in its presentation, and often more difficult to diagnose than a food allergy.

Symptoms of food intolerance vary greatly, and can be mistaken for the symptoms of a food allergy. While true allergies are associated with fast-acting immunoglobulin IgE responses, it can be difficult to determine the offending food causing a food intolerance because the response generally takes place over a prolonged period of time. Thus, the causative agent and the response are separated in time, and may not be obviously related. Food intolerance symptoms usually begin about half an hour after eating or drinking the food in question, but sometimes symptoms may be delayed by up to 48 hours.

Food intolerance can present with symptoms affecting the skin, respiratory tract, gastrointestinal tract (GIT) either individually or in combination. On the skin may include skin rashes, urticaria (hives), angioedema, dermatitis, and eczema. Respiratory tract symptoms can include nasal congestion, sinusitis, pharyngeal irritations, asthma and an unproductive cough. GIT symptoms include mouth ulcers, abdominal cramp, nausea, gas, intermittent diarrhea, constipation, irritable bowel syndrome (IBS),

and may include anaphylaxis.

Food intolerance has been found associated with irritable bowel syndrome and inflammatory bowel disease, chronic constipation, chronic hepatitis C infection, eczema, NSAID intolerance, respiratory complaints, including asthma, rhinitis and headache, functional dyspepsia, eosinophilic esophagitis

and ENT illnesses.

Food hypersensitivity is used to refer broadly to both food intolerances and food allergies. There are a variety of earlier terms which are no longer in use such as "pseudo-allergy".

Food intolerance reactions can include pharmacologic, metabolic, and gastro-intestinal responses to foods or food compounds. Food intolerance does not include either psychological responses or foodborne illness.

A non-allergic food hypersensitivity is an abnormal physiological response. It can be difficult to determine the poorly tolerated substance as reactions can be delayed, dose-dependent, and a particular reaction-causing compound may be found in many foods.

- Metabolic food reactions are due to inborn or acquired errors of metabolism of nutrients, such as in diabetes mellitus, lactase deficiency, phenylketonuria and favism.

- Pharmacological reactions are generally due to low-molecular-weight chemicals which occur either as natural compounds, such as salicylates and amines, or to food additives, such as preservatives, colouring, emulsifiers and taste enhancers. These chemicals are capable of causing drug-like (biochemical) side effects in susceptible individuals.

- Gastro-intestinal reactions can be due to malabsorption or other GI Tract abnormalities.

- Immunological responses are mediated by non-IgE immunoglobulins, where the immune system recognises a particular food as a foreign body.

- Toxins may either be present naturally in food, be released by bacteria, or be due to contamination of food products. Toxic food reactions are caused by the direct action of a food or substance without immune involvement.

- Psychological reactions involve manifestation of clinical symptoms caused not by food but by emotions associated with food. These symptoms do not occur when the food is given in an unrecognisable form.

Elimination diets are useful to assist in the diagnosis of food intolerance. There are specific diagnostic tests for certain food intolerances.