A diagnosis of perioral dermatitis is typically made based on the characteristics of the rash. A skin biopsy is usually not required to make the diagnosis but can be helpful to rule out other skin diseases which may resemble perioral dermatitis. Extended patch testing maybe useful to also rule out allergic contact causes.

Atopic dermatitis is typically diagnosed clinically, meaning it is diagnosed based on signs and symptoms alone, without special testing. Several different forms of criteria developed for research have also been validated to aid in diagnosis. Of these, the UK Diagnostic Criteria, based on the work of Hanifin and Rajka, has been the most widely validated.

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.

Dermatitis herpetiformis is often misdiagnosed, being confused with drug eruptions, contact dermatitis, dishydrotic eczema (dyshidrosis), and even scabies.

The diagnosis can be confirmed by a simple blood test for IgA antibodies against tissue transglutaminase (which cross-react with epidermal transglutaminase), and by a skin biopsy in which the pattern of IgA deposits in the dermal papillae, revealed by direct immunofluorescence, distinguishes it from linear IgA bullous dermatosis and other forms of dermatitis. These tests should be done before the patient starts on a gluten-free diet, otherwise they might produce false negatives. Like in ordinary celiac disease, IgA against transglutaminase disappears (often within months) when patients eliminate gluten from their diet. Thus, for both groups of patients, it may be necessary to restart gluten for several weeks before testing can be done reliably. In 2010, "Cutis" reported an eruption labelled "gluten-sensitive dermatitis" which is clinically indistinguishable from dermatitis herpetiformis but lacks the IgA connection, similar to gastrointestinal symptoms mimicking coeliac disease but without the diagnostic immunological markers.

Perioral dermatitis is likely to fully resolve with short courses of antibiotics but if left untreated it can persist for years and take a chronic form.

Improvement with tetracyclines is usually seen after 4 days and significantly so after 2 weeks.

The classification of exfoliative dermatitis into Wilson-Brocq (chronic relapsing), Hebra or pityriasis rubra (progressive), and Savill (self-limited) types may have had historical value, but it currently lacks pathophysiologic or clinical utility.

There is no good evidence that a mother's diet during pregnancy, the formula used, or breastfeeding changes the risk. There is tentative evidence that probiotics in infancy may reduce rates but it is insufficient to recommend its use.

People with eczema should not get the smallpox vaccination due to risk of developing eczema vaccinatum, a potentially severe and sometimes fatal complication.

Diagnosis of eczema is based mostly on the history and physical examination. In uncertain cases, skin biopsy may be useful. Those with eczema may be especially prone to misdiagnosis of food allergies.

Patch tests are used in the diagnosis of allergic contact dermatitis.

The pathophysiology may involve a mixture of type I and type IV-like hypersensitivity reactions.

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.

Diagnosing allergic contact dermatitis is primarily based on physical exam and medical history. In some cases doctors can establish an accurate diagnosis based on the symptoms that the patient experiences and on the rash's appearance. In the case of a single episode of allergic contact dermatitis, this is all that is necessary. Chronic and/or intermittent rashes which are not readily explained by history and physical exam often will benefit from further testing.

A patch test (contact delayed hypersensitivity allergy test) is a commonly used examination to determine the exact cause of an allergic contact dermatitis. According to the American Academy of Allergy, Asthma, and Immunology, "patch testing is the gold standard for contact allergen identification".

The patch test consists of applying small quantities of potential allergens to small patches and which are then placed on the skin. After two days, they are removed and if a skin reaction occurred to one of the substances applied, a raised bump will be noticeable underneath the patch. The tests are again read at 72 or 96 hours after application.

Patch testing is used for patients who have chronic, recurring contact dermatitis. Other tests that may be used to diagnose contact dermatitis and rule out other potential causes of the symptoms include a skin biopsy and culture of the skin lesion.

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.

You have to treat the primary cause or the exacerbation may persisist and reincide.

Topical steroids are the primary category of medications used to treat exfoliative dermatitis (ED). A sedative antihistamine may be a useful adjunct for pruritic patients, since it helps patients to sleep at night, thus limiting nocturnal scratching and excoriations. Antimicrobial agents often are used if an infection is suspected to be precipitating or complicating exfoliative dermatitis. Other drugs specifically indicated for management of underlying cause of exfoliative dermatitis may be necessary.

The prevalence of nummular dermatitis in the United States is approximately 2 per 1,000. It is considered a disease of adulthood, for it is rare in children.

Diagnosis of nummular dermatitis largely clinical. Biopsies are typically not necessary, and cannot be used to rule out other atopic dermatitis or other eczemas. However, patch testing may be employed to rule out irritants (contact dermatitis) as a cause. In children, nummular dermatitis is commonly confused with tinea corporis.

Most people with rosacea have only mild redness and are never formally diagnosed or treated. No test for rosacea is known.

In many cases, simple visual inspection by a trained health care professional is sufficient for diagnosis. In other cases, particularly when pimples or redness on less-common parts of the face is present, a trial of common treatments is useful for confirming a suspected diagnosis.

The disorder can be confused or co-exist with acne vulgaris or seborrheic dermatitis. The presence of rash on the scalp or ears suggests a different or co-existing diagnosis because rosacea is primarily a facial diagnosis, although it may occasionally appear in these other areas.

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.

Oral antibiotics of the tetracycline class such as minocycline, doxycycline, and tetracycline have been recommended for CGPD. However, their use is limited by side effects such as nausea, vomiting, and sensitivity of the skin to sunlight. Tetracycline antibiotics are not recommended for children under the age of 8 since tetracyclines are known to deposit in teeth (thereby staining them) and impair bone growth in children. The use of calcineurin inhibitor creams such as tacrolimus or pimecrolimus on the skin is controversial and results have been mixed. Certain studies have found the use of topical calcineurin inhibitors led to resolution of CGPD whereas others found incomplete resolution or prolonged symptoms. Topical azelaic acid has also been used successfully to treat CGPD.

Dapsone is an effective treatment in most people. Itching is typically reduced within 2–3 days. However, dapsone treatment has no effect on any intestinal damage that might be present.

Therefore, a strict gluten-free diet must also be followed, and this will usually be a lifelong requirement. This will reduce any associated intestinal damage and the risk of other complications. After some time on a gluten-free diet, the dosage of dapsone can usually be reduced or even stopped, although this can take many years.

Dapsone is an antibacterial, and its role in the treatment of DH, which is not caused by bacteria, is poorly understood. It can cause adverse effects on the blood, so regular blood monitoring is required.

Dapsone is the drug of choice. For individuals with DH unable to tolerate dapsone for any reason, alternative treatment options may include the following:

- colchicine

- lymecycline

- nicotinamide

- tetracycline

- sulfamethoxypyridazine

- sulfapyridine

Some sources claim that diaper rash is more common with cloth diapers. Others claim the material of the diaper is relevant insofar as it can wick and keep moisture away from the baby's skin, and preventing secondary "Candida" infection. However, there may not be enough data from good-quality, randomized controlled trials to support or refute disposable diaper use thus far. Furthermore, the effect of non-biodegradable diapers on the environment is a concerning matter for public policy.

Possible treatments include minimizing diaper use, barrier creams, mild topical cortisones, and antifungal agents. A variety of other inflammatory and infectious processes can occur in the diaper area and an awareness of these secondary types of diaper dermatitis aids in the accurate diagnosis and treatment of patients.

Angular chielitis is normally a diagnosis made clinically. If the sore is unilateral, rather than bilateral, this suggests a local factor ("e.g.", trauma) or a split syphilitic papule. Angular cheilitis caused by mandibular overclosure, drooling, and other irritants is usually bilateral.

The lesions are normally swabbed to detect if Candida or pathogenic bacterial species may be present. Persons with angular cheilitis who wear dentures often also will have their denture swabbed in addition. A complete blood count (full blood count) may be indicated, including assessment of the levels of iron, ferritin, vitamin B12 (and possibly other B vitamins), and folate.

Angular cheilitis could be considered to be a type of cheilitis or stomatitis. Where Candida species are involved, angular cheilitis is classed as a type of oral candidiasis, specifically a primary (group I) Candida-associated lesion. This form angular cheilitis which is caused by Candida is sometimes termed "Candida-associated angular cheilitis", or less commonly, "monilial perlèche". Angular cheilitis can also be classified as acute (sudden, short-lived appearance of the condition) or chronic (lasts a long time or keeps returning), or refractory (the condition persists despite attempts to treat it).

Avoiding triggers that worsen the condition can help reduce the onset of rosacea, but alone will not normally lead to remission except in mild cases. Keeping a journal is sometimes recommended to help identify and reduce food and beverage triggers.

Because sunlight is a common trigger, avoiding excessive exposure to the sun is widely recommended. Some people with rosacea benefit from daily use of a sunscreen; others opt for wearing hats with broad brims. Like sunlight, emotional stress can also trigger rosacea. People who develop infections of the eyelids must practice frequent eyelid hygiene.

Managing pretrigger events such as prolonged exposure to cool environments can directly influence warm room flushing.

Generous application of bland emollients can improve the rash. However, complete resolution will not occur until the lip licking stops. Breaking the cycle of dryness then licking followed by more dryness is key to treatment. Sometimes, unlike in perioral dermatitis, topical steroids may be used for few days only.