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.

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.

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.

If the allergen is encountered and the symptoms are mild, a cold compress can be used to provide relief.

A detailed history allows physicians to determine whether the presenting symptoms are due to an allergen or another source. Diagnostic tests such as conjunctival scrapings to look for eosinophils are helpful in determining the cause of the allergic response. Antihistamines, medication that stabilizes mast cells, and NSAIDs are safe and usually effective. Corticosteroids are reserved for more severe cases of ocular allergy disease, and their use should be monitored by an eye care physician due to possible side-effects. When an allergen is identified, the person should avoid the allergen as much as possible.

During diagnosis it is important to determine the type of hand eczema and plan specific treatment accordingly. An additional diagnosis of allergies will indicate whether contact allergies or atopy diathesis are the cause of the hand eczema. Discussion concerning frequency of contact with water, irritants, and allergens in private and professional environments will also help evaluate individual stresses on the patient's skin. The hands may also exhibit various other skin illnesses and potential fungal infection or psoriasis must be ruled out. Usually, taking the patient’s personal history into account will help provide an accurate diagnosis.

Patch testing has been found to be helpful in the diagnosis of hand eczema.

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

In adults, the prevalence of IgE sensitization to allergens from house dust mite and cat, but not grass, seem to decrease over time as people age. However, the biological reasons for these changes are not fully understood.

Corticosteroids: For years, there was no treatment for atopic eczema. Atopy was believed to be allergic in origin due to the patients’ extremely high serum IgE levels, but standard therapies at the time did not help. Oral prednisone was sometimes prescribed for severe cases. Wet wraps (covering the patients with gauze) were sometimes used in hospitals to control itching. However, the discovery of corticosteroids in the 1950s, and their subsequent incorporation in topical creams and ointments, provided a significant advancement in the treatment of atopic eczema and other conditions. Thus, the use of topical steroids avoided many of the undesirable side-effects of systemic administration of corticosteroids. Topical steroids control the itching and the rash that accompany atopic eczema. Side-effects of topical steroid use are plentiful, and the patient is advised to use topical steroids in moderation and only as needed.

Immune modulators: Pimecrolimus and tacrolimus creams and ointments became available in the 1980s and are sometimes prescribed for atopic eczema. They act by interfering with T cells but have been linked to the development of cancer.

Avoiding dry skin: Dry skin is a common feature of patients with atopic eczema (see also eczema for information) and can exacerbate atopic eczema.

Avoiding allergens and irritants: See eczema for information.

Hand eczema is a common condition: study data indicates a one-year prevalence of up to 10% in the general population. It is estimated that only 50–70% of people affected consult a doctor. The frequency of severe, chronic and recurrent forms of hand eczema is estimated at 5–7%. Approximately 2–4% of hand eczema patients also report that external (topical) therapy is insufficient.

Several factors adversely affect the long-term prognosis, including the development of the condition prior to the 20th birthday, the severity of initial manifestations, and eczema during childhood. Women, especially those under 30, are more frequently affected than men.

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.

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.

Cultures are not often taken or needed as most cases resolve either with time or typical antibiotics. Swabs for bacterial culture are necessary if the history and signs suggest bacterial conjunctivitis but there is no response to topical antibiotics. Viral culture may be appropriate in epidemic case clusters.

A patch test is used to identify the causative allergen in the case where conjunctivitis is caused by allergy.

Conjunctival scrapes for cytology can be useful in detecting chlamydial and fungal infections, allergy, and dysplasia, but are rarely done because of the cost and the general lack of laboratory staff experienced in handling ocular specimens. Conjunctival incisional biopsy is occasionally done when granulomatous diseases ("e.g.", sarcoidosis) or dysplasia are suspected.

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.

The most effective treatment, although not the most practical one, is to discontinue use of diapers, allowing the affected skin to air out. Another option is simply to increase the frequency of diaper changing. Thorough drying of the skin before diapering is a good preventive measure because it is the excess moisture, either from urine and feces or from sweating, that sets the conditions for a diaper rash to occur.

Intertrigo can be diagnosed clinically by a medical professional after taking a thorough history and performing a detailed physical examination. Many other skin conditions can mimic intertrigo's appearance including erythrasmascabies, pyoderma, atopic dermatitis, candidiasis, and seborrheic dermatitis, and fungal infections of the superficial skin caused by "Tinea versicolor" or "Tinea corporis".

Classification can be either by cause or by extent of the inflamed area.

Eyelid dermatitis is commonly related to atopic dermatitis or allergic contact dermatitis. Volatile substances, tosylamide, epoxy hardeners, insect sprays, and lemon peel oil may be implicated, with many cases of eyelid contact dermatitis being caused by substances transferred by the hands to the eyelids.

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 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.

The aim of treatment is to relieve the allergy-induced itch and to remove the fleas from the pet and its home environment. In some cases, secondary bacterial or yeast infections will also need treatment before the itching subsides. Environmental flea control includes using flea foggers or bombs, vacuuming, and treating pet bedding by washing on a hot cycle (over 60 degrees Celsius) in the washing machine. The current on-pet treatment recommended by veterinary dermatologists is spinosad (Comfortis) monthly and nitenpyram (Capstar or generics) every 48 hours until improvement.

Many pets with FAD may also have other allergies, such as allergies to food, contact allergies, and atopic dermatitis.

It can be treated with systemic antiviral drugs, such as aciclovir or valganciclovir. Foscarnet may also be used for immunocompromised host with Herpes simplex and acyclovir-resistant Herpes simplex.

The symptoms of phlyctenular keratoconjunctivitis are primarily treated with application of an appropriate corticosteroid eye drop, such as prednisolone acetate (Pred Forte) or loteprednol (Lotemax). Loteprednol is increasingly preferred due to its lower risk of elevating intraocular pressure. The corticosteroid suppresses the immune response, reducing inflammation and improving most symptoms.

The causative agent (i.e. the source of the antigen that triggered the hypersensitive immune response) should also be identified. "Staphylococcus aureus" is usually the primary suspect, along with "Mycobacterium tuberculosis" in areas where TB is endemic, followed by "Chlamydia trachomatis". Active bacterial infections may be treated with a topical antibiotic or a combination antibiotic-steroid eye drop, such as tobramycin/dexamethasone (Tobradex). An oral tetracycline antibiotic (such as doxycycline) may be used in systemic or particularly severe/intractable infections. Erythromycin may be an effective alternative, especially in pediatric cases where the side effects of tetracyclines are unacceptable.

Artificial tears can reduce dryness and discomfort from corneal lesions. Photophobic discomfort can be mitigated with dark sunglasses.

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.

LSC is typically diagnosed by careful observation and history taking. It is easily recognized (see "signs and symptoms", and "gallery"). Biopsies are not necessary, and cannot be used to distinguish LSC from psoriasis.