Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it. This can be accomplished by having patch tests, one of various methods commonly known as allergy testing. The top three allergens found in patch tests from 2005–06 were: nickel sulfate (19.0%), Myroxylon pereirae (Balsam of Peru, 11.9%), and fragrance mix I (11.5%).

The patient must know where the irritant or allergen is found to be able to avoid it. It is important to also note that chemicals sometimes have several different names, and do not always appear on labels.

The distinction between the various types of contact dermatitis is based on a number of factors. The morphology of the tissues, the histology, and immunologic findings are all used in diagnosis of the form of the condition. However, as suggested previously, there is some confusion in the distinction of the different forms of contact dermatitis. Using histology on its own is insufficient, as these findings have been acknowledged not to distinguish, and even positive patch testing does not rule out the existence of an irritant form of dermatitis as well as an immunological one.

In an industrial setting the employer has a duty of care to its worker to provide the correct level of safety equipment to mitigate exposure to harmful irritants. This can take the form of protective clothing, gloves, or barrier cream, depending on the working environment.

Topical antibiotics should not be used to prevent infection in wounds after surgery. When they are used, it is inappropriate, and the person recovering from surgery is at significantly increased risk of developing contact dermatitis.

Diagnosis is typically obtained by an allergist or other licensed practitioner performing a cold test. During the cold test, a piece of ice is held against the forearm, typically for 3–4 minutes. A positive result is a specific looking mark of raised red hives. The hives may be the shape of the ice, or it may radiate from the contact area of the ice." However, while these techniques assist in diagnosis, they do not provide information about temperature and stimulation time thresholds at which patients will start to develop symptoms."which is essential because it can establish disease severity and monitor the effectiveness of treatment.

Diagnosis of aquagenic urticaria will begin with an evaluation of the patient's clinical history looking for any signs of what might be causing this severe reaction. The patient will then be put to a water treatment test where water will be applied to the upper body for 30 minutes. Water may be placed directly on the skin or a soaked paper towel may be applied. In many cases distilled water, tap water and saline will be used to check for a difference in reaction. After this is removed the skin will be checked for a reaction for the next 10–15 minutes. Because aqugenic urticaria frequently accompanies other types of physical urticaraia, the doctor may perform tests to check for these other conditions. An ice cube may be placed on the forearm for a few minutes to check for cold urticarial, exposure to a hot bath will be used to check for Cholinergis uticaria and the lesions will be inspected to determine the root cause of their appearance.

Evaluations for aquagenic urticaria consist of a clinical history and water challenge test. The standard test for aquagenic urticaria is application of a 35 °C water compress to the upper body for 30 minutes. Water of any temperature can provoke aquagenic urticaria; however, keeping the compress at a similar temperature to that of the human body (37 °C) avoids confusion with cold-induced or local heat urticaria. In addition, a forearm or hand can be immersed in water of varying temperatures. A diagnosis of aquagenic urticaria requires exclusion of other types of physical urticaria, so an exercise test and ice cube test should be performed to rule out other types of physical urticarial. aquagenic urticaria should be distinguished from aquagenic pruritus, in which brief contact with water evokes intense itching without wheals or erythema. The pathogenesis of aquagenic urticaria is not fully known; however, several mechanisms have been proposed. Interaction with water with a component in or on the stratum corneum or sebum, generating a toxic compound, has been suggested. Absorption of this substance would exert an effect of perifollicular mast cell degranulation with release of histamine.

The cause of chronic hives can rarely be determined. In some cases regular extensive allergy testing over a long period of time is requested in hopes of getting new insight. No evidence shows regular allergy testing results in identification of a problem or relief for people with chronic hives. Regular allergy testing for people with chronic hives is not recommended.

This very rare form of angioedema develops in response to contact with vibration. In vibratory angioedema, symptoms develop within two to five minutes after contact with a vibrating object, and abate after about an hour. Patients with this disorder do not suffer from dermographism or pressure urticaria. Vibratory angioedema is diagnosed by holding a vibrating device such as a laboratory vortex machine against the forearm for four minutes. Speedy swelling of the whole forearm extending into the upper arm is also noted later. The principal treatment is avoidance of vibratory stimulants. Antihistamines have also been proven helpful.

Solar urticaria can be difficult to diagnose, but its presence can be confirmed by the process of phototesting. There are several forms of these tests including photopatch tests, phototests, photoprovocation tests, and laboratory tests. All of these are necessary to determine the exact infliction that the patient is suffering from. Photopatch tests are patch tests conducted when it is believed that a patient is experiencing certain symptoms due to an allergy that will only occur when in contact with sunlight. After the procedure, the patient is given a low dosage of UVA radiation.

Another test known as a phototest is the most useful in identifying solar urticaria. In this test, one centimeter segments of skin are subject to varying amounts of UVA and UVB radiation in order to determine the specific dosage of the certain form of radiation that causes the urticaria to form. When testing for its less intense form (fixed solar urticaria), phototesting should be conducted only in the areas where the hives have appeared to avoid the possibility of getting false-negative results.

A third form of testing is the photoprovocation test which is used to identify disorders instigated by sun burns. The process of this test involves exposing one area of a patient's arm to certain dosage of UVB radiation and one area on the other arm to a certain dosage of UVA radiation. The amount of radiation that the patient is exposed to is equal to that "received in an hour of midday summer sun." If the procedure produces a rash, then the patient will undergo a biopsy. Finally, there are laboratory tests which generally involve procedures such as blood, urine, and fecal biochemical tests. In some situations, a skin biopsy may be performed.

Dermographism can be treated by substances (i.e. an antihistamine) which prevent histamine from causing the reaction. These may need to be given as a combination of H antagonists, or possibly with an H-receptor antagonist such as cimetidine.

OTC Vitamin C, 1000 mg daily, increases histamine degradation and removal.

Not taking hot baths or showers may help if it is generalized (all over) and possibly for localized cases (in a specific area). If taking hot showers helps, it may be a condition called shower eczema. If it affects mainly the head, it may be psoriasis. In rare cases, allergy tests may uncover substances the patient is allergic to.

While cromoglycate, which prevents histamine from being released from mast cells, is used topically in rhinitis and asthma, it is not effective orally for treating chronic urticaria.

The more poignant part of this disorder is the lack of desensitization for water and aqua intile injection as allergen even on repeated exposure. Avoidance of allergen as a general principle in any allergic disorder necessitates the evasion of water exposure. Topical application of antihistamines like 1% diphenhydramine before water exposure is reported to reduce the hives. Oil in water emulsion creams, petrolatum as barrier agents for water can be used prior to shower or bath with good control of symptoms. Therapeutic effectiveness of various classes of drugs differs from case to case.

With no particular affinity to any particular ethnic group, seen in all age groups and equally amongst males and females, the precise prevalence is not known.

The causes of a rash are numerous, which may make the evaluation of a rash extremely difficult. An accurate evaluation by a provider may only be made in the context of a thorough history (What medication is the patient taking? What is the patient's occupation? Where has the patient been?) and complete physical examination.

Points to note in the examination include:

- The appearance: "e.g.", purpuric (typical of vasculitis and meningococcal disease), fine and like sandpaper (typical of scarlet fever); circular lesions with a central depression are typical of molluscum contagiosum (and in the past, small pox); plaques with silver scales are typical of psoriasis.

- The distribution: "e.g.", the rash of scarlet fever becomes confluent and forms bright red lines in the skin creases of the neck, armpits and groins (Pastia's lines); the vesicles of chicken pox seem to follow the hollows of the body (they are more prominent along the depression of the spine on the back and in the hollows of both shoulder blades); very few rashes affect the palms of the hands and soles of the feet (secondary syphilis, rickettsia or spotted fevers, guttate psoriasis, hand, foot and mouth disease, keratoderma blennorrhagicum);

- Symmetry: "e.g.", herpes zoster usually only affects one side of the body and does not cross the midline.

A patch test may be ordered, for diagnostic purposes.

Antihistamine agents are the typically prescribed drug for the treatment of physical urticaria. They block the effect of histamine, a compound produced by the body which forms a part of the local immune response consequently causing inflammation. Some research has suggested that the use antihistamines and antagonist in synergy are better for the treatment of physical urticarias.

The cascade of events that link the autoantibody-antigen reaction with the production and release of histamine is not well characterized. Therefore, the focus of treatment for physical urticaria has been on characterizing the effectiveness of antihistamines rather than analysis of receptor binding or the pathomechanisms.

The first-line therapy in ColdU, as recommended by EAACI/GA2 LEN/EDF/WAO guidelines, is symptomatic relief with second-generation H1- antihistamines. if standard doses are ineffective increasing up to 4-fold is recommended to control symptoms.

The second-generation H1-antihistamine, rupatadine, was found to significantly reduce the development of chronic cold urticaria symptom without an increase in adverse effects using 20 and 40 mg.

Allergy medications containing antihistamines such as diphenhydramine (Benadryl), cetirizine (Zyrtec), loratidine (Claritin), cyproheptadine (Periactin), and fexofenadine (Allegra) may be taken orally to prevent and relieve some of the hives (depending on the severity of the allergy). For those who have severe anaphylactic reactions, a prescribed medicine such as doxepin, which is taken daily, should help to prevent and/or lessen the likelihood of a reaction and thus, anaphylaxis. There are also topical antihistamine creams which are used to help relieve hives in other conditions, but there is not any documentation stating it will relieve hives induced by cold temperature.

Cold hives can result in a potentially serious, or even fatal, systemic reaction (anaphylactic shock). People with cold hives may have to carry an injectable form of epinephrine (like Epi-pen or Twinject) for use in the event of a serious reaction.

The best treatment for this allergy is avoiding exposure to cold temperature.

Studies have found that Omalizumab (Xolair) may be an effective and safe treatment to cold urticaria for patient who do not sufficiently respond to standard treatments.

Ebastine has been proposed as an approach to prevent acquired cold urticaria.

Other rashes that occur in a widespread distribution can look like an id reaction. These include atopic dermatitis, contact dermatitis, dyshidrosis, photodermatitis, scabies and drug eruptions.

Solar urticaria, due to its particular features, is considered to be a type of physical urticaria or light sensitivity. Physical urticaria arises from physical factors in the environment, which in the case of solar urticaria is UV radiation or light. SU may be classified based on the wavelength of the radiative energy that causes the allergic reaction; known as Harber's classification, six types have been identified in this system. Type I solar urticaria is caused by UVB (ultraviolet B) radiation, with wavelengths ranging from 290–320 nm. Type II is induced by UVA (ultraviolet A) radiation with wavelengths that can range from 320–400 nm. The wavelength range of type III and IV spans from 400 to 500 nm, while type V can be caused by UVB radiation to visible light (280–600 nm). Type VI has only been known to occur at 400 nm.

Another classification distinguishes two types. The first is a hypersensitivity caused by a reaction to photoallergens located only in people with SU; while the second is caused by photoallergens that can be found in both people with SU and people without it.

A subgroup of solar urticaria, fixed solar urticaria, has also been identified. It is a rare, less intense form of the disease with wheals (swollen areas of the skin) that affect certain, fixed areas of the body. Fixed solar urticaria is induced by a broad spectrum of radiative energy with wavelengths ranging from 300–700 nm.

Symptoms are thought to be the result of histamine being released by mast cells on the surface of the skin. Due to the lack of antigens, histamine causes the skin to swell in affected areas. If the membrane that surrounds the mast cells is too weak it will easily and rapidly break down under physical pressure, which will therefore cause an allergic-like reaction.

Symptoms can be caused or induced by

- stress

- tight or abrasive clothing

- watches

- glasses

- heat

- cold

- anything placing pressure on exposed skin

- infection

The underlying cause of dermatographism is not known, and can last for many years without relief. The condition may subside and be effectively cured; however, it is often a lifelong ailment. It is not a life-threatening disease and is not contagious.

Dermographism may occur in Mastocytosis (systemic mast cell proliferation).

The disease is most often diagnosed as an infant, when parents take their baby in for what appears to be bug bites. The bug bites are actually the clumps of mast cells. Doctors can confirm the presence of mast cells by rubbing the baby's skin. If hives appear, it most likely signifies the presence of urticaria pigmentosa.

Treatment differs according to what rash 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 the affected area, thus rendering the hydrocortisone almost completely ineffective in all except the most mild of cases.

Prevention measures include avoidance of the irritant through its removal from the workplace or through technical shielding by the use of potent irritants in closed systems or automation, irritant replacement or removal and personal protection of the workers.

The cause of physical urticaria is unknown but it has been suggested to be an autoimmune disease. Suggesting that antibodies, which are produced by the immune system to protect humans from foreign microbes, are binding to body tissue; damaging body tissue.

In some cases physical urticaria can be a symptom of an underlying health issue such as:

- thyroid disease

- hepatitis

- infection

- cancer.

Or can also be due to:

- food allergies

- atopy

Prickly heat can be prevented by avoiding activities that induce sweating, using air conditioning to cool the environment, wearing light clothing and in general, avoiding hot and humid weather. Frequent cool showers or cool baths with mild soap can help to prevent heat rash.

The primary remedy for miliaria is to wear lighter clothing, move to a cooler climate, or otherwise avoid overheating one's body. The immediate treatment of the involved skin areas involves the use of a soothing ointment such as calamine lotion.

Medical assistance should be sought for the first episode of a rash with the appearance of miliaria. The differential diagnosis includes several conditions that an experienced practitioner should be able to recognise and may require treatment distinct from the usual measures taken for miliaria. In most cases the rash of miliaria will resolve without intervention. However, severe cases can last for weeks and cause significant disability. General measures should be recommended for all patients, including moving to an air-conditioned environment if possible, avoiding sweat-provoking activities and occlusive clothing, and taking frequent cool showers.

It has been suggested that the use of topical antibacterials (including antibacterial soaps) may shorten the duration of symptoms in miliaria rubra even in the absence of obvious superinfection. Other topical agents that may reduce the severity of symptoms include anti-itch preparations such as calamine or menthol- or camphor-based preparations, and topical steroid creams. However, caution should be used with oil-based preparations (ointments and oily creams as opposed to water-based or aqueous lotions) that may increase blockage to the sweat glands and prolong duration of illness. Other agents have been investigated including supplemental vitamin A and C and vitamin A based medications, but it is worth noting that there is little scientific evidence supporting any of the above treatments in reducing the duration of symptoms or frequency of complications.

In most cases, doctors will recommend that any pimple-like blisters that may form should have the fluid drained out of them (either through in-office procedure or at home in a sterile environment) to avoid the rash from spreading underneath the skin, leading to an increased state of dermatitis. Left untreated, the blisters may spread and take on an increased red appearance, with the fluid inside increasing in viscosity. It is recommended by physicians to sanitize the infected area and then drain the blisters with a sterilized needle or lancet.

In most tropical areas the local dispensaries sell prickly heat powder, a talc admixture containing drying milk proteins (Labilin) and Triclosan to fight the infection. These include cooling menthol to help alleviate difficulty getting to sleep. This is an effective treatment—the powder stays on the skin longer and treats bacteria dispersed into bed linens, providing a reasonably dry refuge area for healing. Miliaria often covers large areas, and generous use of Cortisone may be contraindicated for reasons stated on package warnings. Regular talcum powder will not reduce the rash but can alleviate burning and itching.

In cases where the rash has developed into open blisters or pustular lesions a doctor should be consulted since more aggressive, medically monitored treatment may be required.

Since the cause of the condition cannot be fully avoided in all cases, treatment is usually focused on topical itch management. This can be effected by the application of antipruritic lotions or creams, using phototherapy, or the application of hot or cold packs to the skin after water contact. Paradoxically, hot baths or showers help many patients, possibly because heat causes mast cells in the skin to release their supply of histamine and to remain depleted for up to 24 hours afterward. However, the itching associated with aquagenic pruritus is not clearly caused by histamine; other neurotransmitters, such as substance P, may be involved.

H1 and H2 blockers, such as loratadine, doxepin, or cimetidine, have historically been the first line of pharmacological treatment, but not all sufferers find relief with these medications. When antihistamines do work, loratadine seems to be the most effective for mild cases and doxepin most effective for more severe cases.

Naltrexone, hydrocortisone, or propranolol may relieve itching for some people.

There are no permanent cures for urticaria pigmentosa. However, treatments are possible. Most treatments for mastocytosis can be used to treat urticaria pigmentosa. Many common anti-allergy medications are useful because they reduce the mast cell's ability to react to histamine.

At least one clinical study suggested that nifedipine, a calcium channel blocker used to treat high blood pressure, may reduce mast cell degranulation in patients with urticaria pigmentosa. A 1984 study by Fairly et al. included a patient with symptomatic urticaria pigmentosa who responded to nifedipine at dose of 10 mg po tid. However, nifedipine has never been approved by the FDA for treatment of urticaria pigmentosa.

Another mast cell stabilizer Gastrocrom, a form of cromoglicic acid has also been used to reduce mast cell degranulation.

It was noted that although antihistamines and anti-inflammatory drugs such as, colchicine, sulphasalazine, dapsone, and topical steroid are advocated for in the treatment of DPU, most if not all are unsatisfactory in relieving symptoms. Even a second generation antihistamine, ketotifen, was unable to efficiently and satisfactorily relieve symptoms of DPU