Urushiol causes an eczematous contact dermatitis characterized by redness, swelling, papules, vesicles, blisters, and streaking. People vary greatly in their sensitivity to urushiol. In approximately 15% to 30% of people, urushiol does not trigger an immune system response, while at least 25% of people have a very strong immune response resulting in severe symptoms. Since the skin reaction is an allergic one, people may develop progressively stronger reactions after repeated exposures, or have no immune response on their first exposure but show sensitivity on subsequent exposures.

Approximately 80% to 90% of adults will get a rash if they are exposed to 50 micrograms of purified urushiol. Some people are so sensitive that it only takes a trace of urushiol (two micrograms, or less than one ten-millionth of an ounce) on the skin to initiate an allergic reaction.

The rash takes one to two weeks to run its course and may cause scars, depending on the severity of the exposure. Severe cases involve small (1–2 mm), clear, fluid-filled blisters on the skin. Pus-filled vesicles containing a whitish fluid may indicate an infection. Most poison ivy rashes, without infections, will resolve within 14 days without treatment. Excessive scratching may result in infection, commonly by staphylococcal and streptococcal species; these may require antibiotics.

Contact dermatitis is a localized rash or irritation of the skin caused by contact with a foreign substance. Only the superficial regions of the skin are affected in contact dermatitis. Inflammation of the affected tissue is present in the epidermis (the outermost layer of skin) and the outer dermis (the layer beneath the epidermis).

Contact dermatitis results in large, burning, and itchy rashes. These can take anywhere from several days to weeks to heal. This differentiates it from contact urticaria (hives), in which a rash appears within minutes of exposure and then fades away within minutes to hours. Even after days, contact dermatitis fades only if the skin no longer comes in contact with the allergen or irritant. Chronic contact dermatitis can develop when the removal of the offending agent no longer provides expected relief.

Irritant dermatitis is usually confined to the area where the trigger actually touched the skin, whereas allergic dermatitis may be more widespread on the skin. Symptoms of both forms include the following:

- Red rash. This is the usual reaction. The rash appears immediately in irritant contact dermatitis; in allergic contact dermatitis, the rash sometimes does not appear until 24–72 hours after exposure to the allergen.

- Blisters or wheals. Blisters, wheals (welts), and urticaria (hives) often form in a pattern where skin was directly exposed to the allergen or irritant.

- Itchy, burning skin. Irritant contact dermatitis tends to be more painful than itchy, while allergic contact dermatitis often itches.

While either form of contact dermatitis can affect any part of the body, irritant contact dermatitis often affects the hands, which have been exposed by resting in or dipping into a container (sink, pail, tub, swimming pools with high chlorine) containing the irritant.

The symptoms of allergic contact dermatitis are very similar to the ones caused by irritant contact dermatitis, which makes the first even harder to diagnose. The first sign of allergic contact dermatitis is the presence of the rash or skin lesion at the site of exposure. Depending on the type of allergen causing it, the rash can ooze, drain or crust and it can become raw, scaled or thickened. Also, it is possible that the skin lesion does not take the form of a rash but it may include papules, blisters, vesicles or even a simple red area. The main difference between the rash caused by allergic contact dermatitis and the one caused by irritant contact dermatitis is that the latter tends to be confined to the area where the trigger touched the skin, whereas in allergic contact dermatitis the rash is more likely to be more widespread on the skin. Another characteristic of the allergic contact dermatitis rash is that it usually appears after a day or two after exposure to the allergen, unlike irritant contact dermatitis that appears immediately after the contact with the trigger.

Other symptoms may include itching, skin redness or inflammation, localized swelling and the area may become more tender or warmer. If left untreated, the skin may darken and become leathery and cracked. Pain can also be present.

The symptoms of allergic contact may persist for as long as one month before resolving completely. Once an individual has developed a skin reaction to a certain substance it is most likely that they will have it for the rest of their life, and the symptoms will reappear when in contact with the allergen.

Dermatitis symptoms vary with all different forms of the condition. They range from skin rashes to bumpy rashes or including blisters. Although every type of dermatitis has different symptoms, there are certain signs that are common for all of them, including redness of the skin, swelling, itching and skin lesions with sometimes oozing and scarring. Also, the area of the skin on which the symptoms appear tends to be different with every type of dermatitis, whether on the neck, wrist, forearm, thigh or ankle. Although the location may vary, the primary symptom of this condition is itchy skin. More rarely, it may appear on the genital area, such as the vulva or scrotum. Symptoms of this type of dermatitis may be very intense and may come and go. Irritant contact dermatitis is usually more painful than itchy.

Although the symptoms of atopic dermatitis vary from person to person, the most common symptoms are dry, itchy, red skin. Typical affected skin areas include the folds of the arms, the back of the knees, wrists, face and hands. Perioral dermatitis refers to a red bumpy rash around the mouth.

Dermatitis herpetiformis symptoms include itching, stinging and a burning sensation. Papules and vesicles are commonly present. The small red bumps experienced in this type of dermatitis are usually about 1 cm in size, red in color and may be found symmetrically grouped or distributed on the upper or lower back, buttocks, elbows, knees, neck, shoulders, and scalp. Less frequently, the rash may appear inside the mouth or near the hairline.

The symptoms of seborrheic dermatitis, on the other hand, tend to appear gradually, from dry or greasy scaling of the scalp (dandruff) to scaling of facial areas, sometimes with itching, but without hair loss. In newborns, the condition causes a thick and yellowish scalp rash, often accompanied by a diaper rash. In severe cases, symptoms may appear along the hairline, behind the ears, on the eyebrows, on the bridge of the nose, around the nose, on the chest, and on the upper back.

Urushiol-induced contact dermatitis (also called Toxicodendron dermatitis and Rhus dermatitis) is the medical name given to allergic rashes produced by the oil urushiol, which is contained in various plants, most notably those of the "Toxicodendron" genus: the Chinese lacquer tree, poison ivy, poison oak, and poison sumac. The name is derived from the Japanese word for the sap of the Chinese lacquer tree, "urushi". Other plants in the sumac family (including mango, pistachio, the Burmese lacquer tree, the India marking nut tree, and the shell of the cashew) also contain urushiol, as do unrelated plants such as "Ginkgo biloba."

As is the case with all contact dermatitis, urushiol-induced rashes are a Type IV hypersensitivity reaction, also known as delayed-type hypersensitivity. Symptoms include itching, inflammation, oozing, and, in severe cases, a burning sensation.

The American Academy of Dermatology estimates that there are up to 50 million cases of urushiol-induced dermatitis annually in the United States alone, accounting for 10% of all lost-time injuries in the United States Forest Service. Poison oak is a significant problem in the rural Western and Southern United States, while poison ivy is most rampant in the Eastern United States. Dermatitis from poison sumac is less common.

Discoid eczema (nummular eczema, exudative eczema, microbial eczema) is characterized by round spots of oozing or dry rash, with clear boundaries, often on lower legs. It is usually worse in winter. Cause is unknown, and the condition tends to come and go. (ICD-10 L30.0)

Contact dermatitis is a type of inflammation of the skin.

It results from either exposure to allergens (allergic contact dermatitis) or irritants (irritant contact dermatitis). Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight. Diagnosis of allergic contact dermatitis can often be supported by patch testing.

Allergic contact dermatitis (ACD) is a form of contact dermatitis that is the manifestation of an allergic response caused by contact with a substance; the other type being irritant contact dermatitis (ICD).

Although less common than ICD, ACD is accepted to be the most prevalent form of immunotoxicity found in humans. By its allergic nature, this form of contact dermatitis is a hypersensitive reaction that is atypical within the population. The mechanisms by which these reactions occur are complex, with many levels of fine control. Their immunology centres on the interaction of immunoregulatory cytokines and discrete subpopulations of T lymphocytes.

Hand eczema presents on the palms and soles, and may sometimes be difficult or impossible to differentiate from atopic dermatitis, allergic contact dermatitis, and psoriasis, which also commonly involve the hands. Even a biopsy of all these conditions may not result in a definitive diagnosis, as all three conditions may demonstrate spongiosis and crusting on the hands.

Non-communicable inflammation of the skin of the hands is referred to as hand eczema. Hand eczema is widely prevalent and, as it is a very visible condition associated with severe itching or pain, has serious consequences for the affected person including a high psychological impact. Different disease patterns can be identified according to the course of the illness, appearance of symptoms, degree of severity, or catalysts. Prognosis is hard to predict for individual cases of chronic hand eczema and usually differs from patient to patient. Successful treatment depends on determining the causes of the condition, obtaining an accurate diagnosis, sustainable hand protection procedures and an early, extensive, and where appropriate internal treatment.

Normally, skin inflammation connected with hand eczema is accompanied by blister formation and pronounced itching, but solid calluses and painful tearing may also occur. The quality of life of the affected person is seriously diminished, especially in the case of chronic forms of the illness, and psychological impact is often very high. This impact is enhanced by the high visibility of the illness on the hands, which may lead to feelings of shame and fear of rejection.

Photodermatitis may result in swelling, difficulty breathing, a burning sensation, a red itchy rash sometimes resembling small blisters, and peeling of the skin. Nausea may also occur. There may also be blotches where the itching may persist for long periods of time. In these areas an unsightly orange to brown tint may form, usually near or on the face.

Dyshidrosis has been described as having the following characteristics:

- Itchiness of the palms or soles, followed the a sudden development of intensely itchy small blisters on the sides of the fingers, the palms or the feet.

- These blisters are often described as having a "tapioca pudding" appearance.

- After a few weeks, the small blisters eventually disappear as the top layer of skin falls off.

- These eruptions do not occur elsewhere on the body.

- The eruptions may be symmetrical.

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.

Irritant contact dermatitis is a form of contact dermatitis that can be divided into forms caused by chemical irritants and those caused by physical irritants.

A stinging and burning sensation with rash is often felt and noticed, but itching is less common. Often the rash is steroid responsive, initially improving with application of topical steroid. The redness caused by perioral dermatitis has been associated with variable level of depression.

Initially, there may be small pinpoint papule either side of the nostrils. Multiple small (1-2mm) papules and pustules then occur around the mouth, nose and sometimes cheeks. The area of skin directly adjacent to the lips, also called the vermillion border, is spared and looks normal. There may be some mild background redness and occasional scale. These areas of skin are felt to be drier and therefore there is a tendency to moisturise them more frequently. Hence, they do not tolerate drying agents well and the rash can be worsened by them.

Perioral dermatitis is also known by other names including rosacea-like dermatoses, periorofacial dermatitis and periorificial dermatitis.

Unlike rosacea which involves mainly the nose and cheeks, there is no telangiectasia in perioral dermatitis. Rosacea also has a tendency to be present in older people. Acne can be distinguished by the presence of comedones and by its wider distribution on the face and chest. There are no comedones in personal dermatitis.

Other skin diseases which may resemble perioral dermatitis include:

- Rosacea

- Acne vulgaris

- Seborrheic dermatitis

- Allergic contact dermatitis

- Irritant contact dermatitis

Nickel allergy (also referred to as Ni-ACD) is a form of allergic contact dermatitis (ACD) caused by exposure to the chemical element nickel.

Type IV allergy, also known as allergic contact dermatitis, involves a delayed skin rash that is similar to poison ivy with blistering and oozing of the skin ("see urushiol-induced contact dermatitis"). It can be diagnosed through a positive skin patch test, although a negative test does not rule out a latex allergy.

Severe irritation takes place if a latex catheter is inserted in the urinary tract of a person allergic to latex. That is especially severe in case of a radical prostatectomy due to the open wound there and the exposure lasting e.g. two weeks. Intense pain may indicate such situation.

Garlic allergy or allergic contact dermatitis to garlic is a common inflammatory skin condition caused by contact with garlic oil or dust. It mostly affects people who cut and handle fresh garlic, such as chefs, and presents on the tips of the thumb, index and middle fingers of the non-dominant hand (which typically hold garlic bulbs during the cutting). The affected fingertips show an asymmetrical pattern of fissure as well as thickening and shedding of the outer skin layers, which may progress to second- or third-degree burn of injured skin.

Garlic dermatitis is similar to the tulip dermatitis and is induced by a combined mechanical and chemical action. Whereas the former mechanism acts via skin rubbing which progresses into damage, the major cause of the latter is the chemical diallyl disulfide (DADS), together with related compounds allyl propyl disulfide and allicin. These chemicals occur in oils of plants of the genus "Allium", including garlic, onion and leek.

Garlic allergy has been known since at least 1950. It is not limited to hand contact, but can also be induced, with different symptoms, by inhaling garlic dust or ingesting raw garlic, though the latter cases are relatively rare. DADS penetrates through most types of commercial gloves, and thus wearing gloves while handling garlic has proven inefficient against the allergy. Treatment includes avoiding any contact with garlic oil or vapours, as well as medication, such as administering acitretin (25 mg/day, orally) or applying psoralen and ultraviolet light to the affected skin area over a period of 12 weeks (PUVA therapy).

Flea allergy dermatitis, FAD, is an eczematous itchy skin disease of dogs and cats. For both of these domestic species, flea allergy dermatitis is the most common cause of skin disease. Affected animals develop allergic reactions to chemicals in flea saliva. Symptoms of this reaction include erythema (redness), papules (bumps), pustules (pus-filled bumps), and crusts (scabs). If severe, hair loss will occur in the affected area. Dogs with flea allergy dermatitis often show hair loss and eczematous skin rash on the lower back, upper tail, neck, and down the back of the legs. Cats with flea allergy dermatitis may develop a variety of skin problems, including feline eosinophilic granuloma, miliary dermatitis, or self-inflicted alopecia from excessive grooming.

Once pederin is on the skin from the initial beetle contact, it may also be spread elsewhere on the skin. "Kissing" or "mirror-image" lesions where two skin areas come in contact (for example, the elbow flexure) are often seen. Washing the hands and skin with soap and water is strongly recommended, if contact with a rove beetle has occurred.

Initial skin contact with pederin shows no immediate result. Within 12–36 hours, however, a reddish rash (erythema) appears, which develops into blisters. Irritation, including crusting and scaling, may last from two to three weeks.

One study reported best results with a treatment regimen that combined topical steroids with oral antihistamines and antibiotics. The authors hypothesized that antibiotics were helpful because of the possible contamination of skin by pederin-producing bacteria.

Natural rubber latex can also cause irritant contact dermatitis, a less severe form of reaction that does not involve the immune system. Contact dermatitis causes dry, itchy, irritated areas on the skin, most often on the hands. Latex-glove induced dermatitis increases the chance of hospital-acquired infections, including blood-borne infections, being transmitted.

Dyshidrosis, is a type of dermatitis, that is characterized by itchy blisters on the palms of the hands and bottoms of the feet. Blisters are generally one to two millimeters in size and heal over three weeks. However, they often recur. Redness is not usually present. Repeated attacks may result in fissures and skin thickening.

The cause is unknown. Triggers may include allergens, physical or mental stress, frequent hand washing, or metals. Diagnosis is typically based on what it looks like and the symptoms. Allergy testing and culture may be done to rule out other problems. Other conditions that produce similar symptoms include pustular psoriasis and scabies.

Avoiding triggers may be useful as may a barrier cream. Treatment is generally with steroid cream. High strength steroid creams may be required for the first week or two. Antihistamines may be used to help with the itch. If this is not effective steroid pills, tacrolimus, or psoralen plus ultraviolet A (PUVA) may be tried.

About 1 in 2,000 people are affected in Sweden. Males and females appear to be affected equally. It explains about one in five cases of hand dermatitis. The first description was in 1873. The name comes from the word "dyshidrotic," meaning "difficult sweating," as problems with sweating was once believed to be the cause.

Perioral dermatitis is a type of skin rash. Symptoms include multiple small (1–2 mm) bumps and blisters with sometimes background redness and scale, localized to the skin around the mouth and nostrils. Less commonly the eyes and genitalia may be involved. It can be persistent or recurring and resembles particularly rosacea and to some extent acne and allergic dermatitis. The term dermatitis is a misnomer because this is not an eczematous process.

The cause is unclear. Topical steroids are associated with the condition and moisturizers and cosmetics may contribute. The underlying mechanism may involve blockage of the skin surface followed by subsequent excessive growth of skin flora. Fluorinated toothpaste and some micro-organisms including candida may also worsen the condition, but their roles in this condition is unclear. It is considered a disease of the hair follicle with biopsy samples showing microscopic changes around the hair follicle. Diagnosis is based on symptoms.

Treatment is typically by stopping topical steroids, changing cosmetics, and in more severe cases, taking tetracyclines by mouth. Stopping steroids may initially worse the rash. The condition is estimated to affect 0.5-1% of people a year in the developed world. Up to 90% of those affected are women between the ages of 16 and 45 years, though it also affects children and the elderly, and has an increasing incidence in men.

Photodermatitis, sometimes referred to as sun poisoning or photoallergy, is a form of allergic contact dermatitis in which the allergen must be activated by light to sensitize the allergic response, and to cause a rash or other systemic effects on subsequent exposure. The second and subsequent exposures produce photoallergic skin conditions which are often eczematous.

Nummular dermatitis is characterized by chronic or relapsing itchy coin-sized ovoid-shaped red plaques. They can occur on the trunk, limbs, face, and hands.