According to the hygiene hypothesis, when children are brought up exposed to allergens in the environment at a young age, their immune system is more likely to tolerate them, while children brought up in a modern "sanitary" environment are less likely to be exposed to those allergens at a young age, and, when they are finally exposed, develop allergies. There is some support for this hypothesis with respect to AD. Those exposed to dogs while growing up have a lower risk of atopic dermatitis. There is also support from epidemiological studies for a protective role for helminths against AD. Likewise children with poor hygiene are at a lower risk for developing AD, as are children who drink unpasteurised milk.

In a small percentage of cases, atopic dermatitis is caused by sensitization to foods. Also, exposure to allergens, either from food or the environment, can exacerbate existing atopic dermatitis. Exposure to dust mites, for example, is believed to contribute to one's risk of developing AD. A diet high in fruits seems to have a protective effect against AD, whereas the opposite seems true for fast foods. Atopic dermatitis sometimes appears to be associated with celiac disease and non-celiac gluten sensitivity, and the improvement with a gluten-free diet indicates that gluten is a causative agent in these cases.

The exact causes of dyshidrosis are unknown. In 2013, a randomized, double-blind, placebo-controlled cross-over study by the University Medical Center Groningen reported that dyshydrosis outbreaks on the hands increased significantly among those allergic to house dust mites, following inhalation of house dust mite allergen.

Food allergens may be involved in certain cases. Cases studies have implicated a wide range of foods including tuna, tomato, pineapple, chocolate, coffee, and spices among others. A number of studies have implicated balsam of Peru.

Id reaction and irritant contact dermatitis are possible causes.

Cosmetics play an important role as causal factors for perioral dermatitis. Regular generous applications of moisturising creams cause persistent hydration of the horny layer causing impairment and occlusion of the barrier function, irritation of the hair follicle and proliferation of skin flora. Combining this with night cream and foundation significantly increases risk of perioral dermatitis by 13-fold.

Reports of perioral dermatitis in renal transplant recipients treated with oral corticosteroids and azathioprine have been documented.

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.

Although wetness alone has the effect of macerating the skin, softening the stratum corneum, and greatly increasing susceptibility to friction injury, urine has an additional impact on skin integrity because of its effect on skin pH. While studies show that ammonia alone is only a mild skin irritant, when urea breaks down in the presence of fecal urease it increases pH because ammonia is released, which in turn promotes the activity of fecal enzymes such as protease and lipase. These fecal enzymes increase the skin's hydration and permeability to bile salts which also act as skin irritants.

There is no detectable difference in rates of diaper rash in conventional disposable diaper wearers and reusable cloth diaper wearers. "Babies wearing superabsorbent disposable diapers with a central gelling material have fewer episodes of diaper dermatitis compared with their counterparts wearing cloth diapers. However, keep in mind that superabsorbent diapers contain dyes that were suspected to cause allergic contact dermatitis (ACD)." Whether wearing cloth or disposable diapers they should be changed frequently to prevent diaper rash, even if they don't feel wet. To reduce the incidence of diaper rash, disposable diapers have been engineered to pull moisture away from the baby's skin using synthetic non-biodegradable gel. Today, cloth diapers use newly available superabsorbent microfiber cloth placed in a pocket with a layer of light permeable material that contacts the skin. This design serves to pull moisture away from the skin in to the microfiber cloth. This technology is used in most major pocket cloth diapers brands today.

The interaction between fecal enzyme activity and IDD explains the observation that infant diet and diaper rash are linked because fecal enzymes are in turn affected by diet. Breast-fed babies, for example, have a lower incidence of diaper rash, possibly because their stools have higher pH and lower enzymatic activity. Diaper rash is also most likely to be diagnosed in infants 8–12 months old, perhaps in response to an increase in eating solid foods and dietary changes around that age that affect fecal composition. Any time an infant’s diet undergoes a significant change (i.e. from breast milk to formula or from milk to solids) there appears to be an increased likelihood of diaper rash.

The link between feces and IDD is also apparent in the observation that infants are more susceptible to developing diaper rash after treating with antibiotics, which affect the intestinal microflora. Also, there is an increased incidence of diaper rash in infants who have suffered from diarrhea in the previous 48 hours, which may be because fecal enzymes such as lipase and protease are more active in feces which have passed rapidly through the gastrointestinal tract.

Most cases are well managed with topical treatments and ultraviolet light. About 2% of cases are not. In more than 60% of young children, the condition subsides by adolescence.

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.

Irritant contact dermatitis (ICD) can be divided into forms caused by chemical irritants, and those caused by physical irritants. Common chemical irritants implicated include: solvents (alcohol, xylene, turpentine, esters, acetone, ketones, and others); metalworking fluids (neat oils, water-based metalworking fluids with surfactants); latex; kerosene; ethylene oxide; surfactants in topical medications and cosmetics (sodium lauryl sulfate); and alkalis (drain cleaners, strong soap with lye residues).

Physical irritant contact dermatitis may most commonly be caused by low humidity from air conditioning. Also, many plants directly irritate the skin.

If the condition thickens, turns red and irritated, starts spreading, appears on other body parts, or if the baby develops thrush (fungal mouth infection), fungal ear infection (an ear infection that does not respond to antibiotics) or a persistent diaper rash, medical intervention is recommended.

Severe cases of cradle cap, especially with cracked or bleeding skin, can provide a place for bacteria to grow. If the cradle cap is caused by a fungal infection which has worsened significantly over days or weeks to allow bacterial growth (impetigo, most commonly), a combination treatment of antibiotics and antifungals may be necessary. Since it is difficult for a layperson to distinguish the difference between sebaceous gland cradle cap, fungal cradle cap, or either of these combined with a bacterial infection, medical advice should be sought if the condition appears to worsen.

Cradle cap is occasionally linked to immune disorders. If the baby is not thriving and has other problems (e.g. diarrhea), a doctor should be consulted.

About 1 in 2,000 people are affected in Sweden. Males and females appear to be affected equally.

Assurances that this condition will clear as the baby matures are very common. However, studies have shown that the condition occasionally persists into the toddler years, and less commonly into later childhood. It tends to recur in adolescence and persists into adulthood. In an Australian study, about 15 percent of previously diagnosed children still had eczema 10 years later. Sometimes, cradle cap turns into atopic dermatitis. Rarely, it turns out to be misdiagnosed psoriasis.

Allergic contact dermatitis (ACD) is accepted to be the most prevalent form of immunotoxicity found in humans, and is a common occupational and environmental health problem. By its allergic nature, this form of contact dermatitis is a hypersensitive reaction that is atypical within the population. The mechanisms by which this reaction occurs are complex, with many levels of fine control. Their immunology centres on the interaction of immunoregulatory cytokines and discrete subpopulations of T lymphocytes.

Allergens include nickel, gold, Balsam of Peru ("Myroxylon pereirae"), chromium, and the oily coating from plants of the "Toxicodendron" genus, such as poison ivy, poison oak, and poison sumac.

The main cause is a type-I hypersensitivity reaction to products containing abietic acid, such as the rosin/colophony, which is commonly used as a friction-increasing agent. Players of bowed string instruments (violin, viola, cello, double bass) rub cakes or blocks of rosin on their bow so it can grip the strings. Ballet and flamenco dancers sometimes rub their shoes in powdered rosin to reduce slippage before going on stage. Gymnasts, baseball pitchers and ten pin bowlers use rosin to improve grip. Common locations of this contact dermatitis are hands, face and neck.

Treatment may include corticoids, astringents, and keratolytics. Dermatoses tend to be recurrent unless the use or contact can be avoided. Discontinuation of the instrument is curative in almost all cases, but usually impractical.

Common allergens implicated include the following:

- Nickel (nickel sulfate hexahydrate) – has been recognized as a significant cause of allergy. This metal is frequently encountered in stainless steel cookware, jewelry and clasps or buttons on clothing. Current estimates gauge are that roughly 2.5 million US adults and 250,000 children suffer from nickel allergy, which costs an estimated $5.7 billion per year for treatment of symptoms. A significant portion of nickel allergy is preventable.

- Gold (gold sodium thiosulfate) – precious metal often found in jewelry and dental materials

- Balsam of Peru (Myroxylon pereirae) – used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items for healing properties; derived from tree resin. It may also be a component of artificial vanilla and/or cinnamon flavorings.

- Chromium – used in the tanning of leather. Also a component of uncured cement/mortar, facial cosmetics and some bar soaps.

- Urushiol – oily coating from plants of Toxicodendron genus – poison ivy, poison oak, and poison sumac. Also found in mango plants and cashews.

- Sap from certain species of mangrove and agave

- Thiomersal – mercury compound used in local antiseptics and in vaccines

- Neomycin – topical antibiotic common in first aid creams and ointments, cosmetics, deodorant, soap, and pet food. Found by itself, or in Neosporin or Triple Antibiotic

- Fragrance mix – group of the eight most common fragrance allergens found in foods, cosmetic products, insecticides, antiseptics, soaps, perfumes, and dental products

- Formaldehyde – preservative with multiple uses, "e.g.", in paper products, paints, medications, household cleaners, cosmetic products, and fabric finishes. Often released into products by the use of formaldehyde releasers such as imidazolidinyl urea, diazolidinyl urea, Quaternium-15, DMDM Hydantoin, and 2-bromo-2-nitropropane-1,3-diol.

- Cobalt chloride – metal found in medical products; hair dye; antiperspirant; metal-plated objects such as snaps, buttons or tools; and in cobalt blue pigment

- Bacitracin – topical antibiotic found by itself, or as Polysporin or Triple Antibiotic

- Quaternium-15 – preservative in cosmetic products (self-tanners, shampoo, nail polish, sunscreen) and in industrial products (polishes, paints and waxes).

- Colophony (Rosin) – rosin, sap or sawdust typically from spruce or fir trees

- Topical steroid – "see" steroid allergy

- Photographic developers, especially those containing metol

- Topical anesthetics – such as pramoxine or diphenhydramine, after prolonged use

- Isothiazolinones – preservatives used in many personal care, household, and commercial products.

- Mercaptobenzothiazole – in rubber products, notably shoes, gloves, and car tires.

- Soluble salts of platinum – "see" platinosis

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.

Rosin, the material commonly used to wax string instruments is known to cause allergic contact dermatitis in musicians. Nickel, a metal found in musical instruments causes allergic contact dermatitis on the fingers and hands of string instrumentalists and in the lip and neck of wind instrumentalists. Wind instrumentalists with lip and neck infection should switch to gold or plastic mouthpieces if allergic dermatitis occurs. (R)-4-methoxydalbergione present in rosewood may cause allergic contact dermatitis in violinists. Cane reed (causing chelitis in saxophone players), propolis (a wax used to close structural gaps in musical instruments), paraphenylenediamine (used to polish musical instruments) and potassium dichromate (tanning agent to the skin of the harp) also cause allergic contact dermatitis in musicians.

Many contact sensitizers or irritants are known to cause contact dermatitis superimposed on nummular dermatitis. Studies have implicated nickel, cobalt, chromate, and fragrance as likely culprits. Xerosis, or dehydration of skin is also a likely cause. Infection with "Staphylococcus aureus" bacteria or "Candida" may also play a role.

Chemical irritant contact dermatitis is either acute or chronic, which is usually associated with strong and weak irritants respectively. The following definition is provided by Mathias and Maibach (1978): The mechanism of action varies. Detergents, surfactants, extremes of pH, and organic solvents all directly affecting the barrier properties of the epidermis. These effects include removing fat emulsion, defatting of dermal lipids, inflicting cellular damage on the epithelium, and increasing the transepidermal water loss by damaging the horny layer water-binding mechanisms and damaging the DNA, which causes the layer to thin. Concentrated irritants have an acute effect, but this is not as common as the accumulative, chronic effect of irritants whose deleterious effects build up with subsequent doses (ESCD 2006).

Chemical irritants are often strong alkalis as found in drain cleaners and soap with lye residues. Many other chemical compounds can also cause contact dermatitiis.

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.

Occupational skin diseases are ranked among the top five occupational diseases in many countries.

Contact Dermatitis due to irritation is inflammation of the skin which results from a contact with an irritant. It has been observed that this type of dermatitis does not require prior sensitization of the immune system. There have been studies to support that past or present atopic dermatitis is a risk factor for this type of dermatitis. Common irritants include detergents, acids, alkalies, oils, organic solvents and reducing agents.

The acute form of this dermatitis develops on exposure of the skin to a strong irritant or caustic chemical. This exposure can occur as a result of accident at a workplace . The irritant reaction starts to increase in its intensity within minutes to hours of exposure to the irritant and reaches its peak quickly. After the reaction has reached its peak level, it starts to heal. This process is known as decrescendo phenomenon. The most frequent potent irritants leading to this type of dermatitis are acids and alkaline solutions. The symptoms include redness and swelling of the skin along with the formation of blisters.

The chronic form occurs as a result of repeated exposure of the skin to weak irritants over long periods of time.

Clinical manifestations of the contact dermatitis are also modified by external factors such as environmental factors (mechanical pressure, temperature, and humidity) and predisposing characteristics of the individual (age, sex, ethnic origin, preexisting skin disease, atopic skin diathesis, and anatomic region exposed.

Another occupational skin disease is glove-related hand urticaria, believed to be caused by repeated wearing and removal of the gloves. It has been reported as an occupational problem among the health care workers. The reaction is caused by the latex or the nitrile present in the gloves.

Atopy is a hereditary and chronic (lifelong) allergic skin disease. Signs usually begin between 6 months and 3 years of age, with some breeds of dog, such as the Golden Retriever showing signs at an earlier age. Dogs with atopic dermatitis are itchy, especially around the eyes, muzzle, ears and feet. In severe cases the irritation is generalised. If the allergens are seasonal, the signs of irritation are similarly seasonal. Many dogs with house dust mite allergy have perennial disease. Some of the allergens associated with atopy in dogs include pollens of trees, grasses and weeds, as well as molds and House dust mite. Ear and skin infections with the bacteria "Staphylococcus pseudintermedius" and the yeast "Malassezia pachydermatis" are common secondary to atopic dermatitis.

Food allergy can be associated with identical signs and some authorities consider food allergy to be a type of atopic dermatitis.

Diagnosis of atopic dermatitis is by elimination of other causes of irritation including fleas, scabies and other parasites such as Cheyletiella and lice. Food allergy can be identified through the use of elimination diet trials in which a novel or hydrolysed protein diet is used for a minimum of 6 weeks and allergies to aeroallergens can be identified using intradermal allergy testing and/or blood testing (allergen-specific IgE ELISA).

Treatment includes avoidance of the offending allergens if possible, but for most dogs this is not practical or effective. Other treatments modulate the adverse immune response to allergens and include antihistamines, steroids, ciclosporin and immunotherapy (a process in which allergens are injected to try to induce tolerance). In many cases shampoos, medicated wipes and ear cleaners are needed to try to prevent the return of infections.

New research into T-cell receptor peptides and their effects on dogs with severe, advanced atopic dermatitis are being investigated.