What is irritant contact dermatitis

Irritant contact dermatitis is a form of contact dermatitis, in which the skin is injured by friction, environmental factors such as cold, over-exposure to water, or chemicals such as acids, alkalis, detergents and solvents. Irritants include such everyday things as water, detergents, solvents, acids, alkalis, adhesives, metalworking fluids and friction. Often several of these act together to injure the skin. Irritant contact dermatitis may affect anyone, given sufficient exposure to irritants, but those with atopic dermatitis are particularly susceptible. 80% of cases of occupational hand dermatitis are due to irritants, most often affecting cleaners, hairdressers and food handlers.

Irritant contact dermatitis is a nonspecific inflammatory eczematous skin disease to direct chemical damage that releases mediators of inflammation predominantly from epidermal cells ¹. Irritant contact dermatitis is caused by chemicals or metal ions that exert toxic effects without inducing a T-cell response (contact irritants) or by small reactive chemicals that modify proteins and induce innate and adaptive immune responses (contact allergens) ².

The likelihood of developing irritant contact dermatitis increases with the duration, intensity, and concentration of the substance. Chemical or physical agents and microtrauma may produce skin irritation thus causing irritant contact dermatitis ¹. Physical irritants like friction, abrasions, occlusion, and detergents like sodium lauryl sulfate produce more irritant contact dermatitis in combination than alone ³.

The factors which determine the severity of irritant contact dermatitis include quantity and concentration of the irritant, duration, and frequency of exposure ¹. It also depends on the type of skin if it is thick, thin, oily, dry, very fair, previously damaged skin, or having a pre-existing atopic tendency. Environmental factors like high or low temperature and humidity also determine the severity ¹.

Irritant contact dermatitis can appear similar to other forms of dermatitis, notably:

• All kinds of hand dermatitis
• Allergic contact dermatitis — this is caused by an immune response following skin contact with an allergenic substance. Small quantities may be sufficient to cause allergy, whereas a certain minimum exposure is necessary for irritant contact dermatitis. Irritant and allergic contact dermatitis may coexist.
• Pompholyx eczema (dyshidrotic eczema) — in which there are itchy clusters of blisters along the sides of the fingers and on the palms, often triggered by sweating.

Sometimes it is easy to recognize irritant contact dermatitis, and no specific tests are necessary. The rash usually heals once the irritant is removed and, if necessary, special treatment is applied. While some tests can indicate the irritant potential of substances, there are no specific tests that can reliably show what the effect of an irritant will be in each case. Irritant dermatitis is usually the result of the cumulative impact of multiple irritants.

Irritant contact dermatitis vs Allergic contact dermatitis

Allergic contact dermatitis is a form of dermatitis/eczema caused by an allergic reaction to a material, called an allergen, in contact with the skin. The allergen is harmless to people that are not allergic to it. Allergic contact dermatitis is also called contact allergy. Common allergens for allergic contact dermatitis are nickel, balsam of Peru, chromium, neomycin, formaldehyde, thiomersal, fragrance mix, cobalt, and parthenium ⁴.

Common allergens causing allergic contact dermatitis include the following:

• Paraphenylenediamine (PPD) present in hair dye; common cause of allergic contact dermatitis on the scalp, face, ears
• Neomycin and bacitracin applied to the areas of stasis dermatitis and leg ulcers may be the cause of allergic contact dermatitis on the legs and feet
• Topical neomycin and corticosteroids can lead to allergic contact dermatitis in patients with otitis externa
• In women with lichen sclerosus et atrophicus, benzocaine applied in pruritus ani and pruritus vulvae may develop allergic contact dermatitis
• Nickel is the most common metal present in artificial jewelry which is the cause of allergic contact dermatitis.

Allergic contact dermatitis is a type 4 or delayed hypersensitivity reaction and occurs 48–72 hours after exposure to the allergen ¹. The mechanism involves CD4+ T-lymphocytes, which recognise an antigen on the skin surface, releasing cytokines that activate the immune system and cause the dermatitis. Note:

• Contact allergy occurs predominantly from an allergen on the skin rather than from internal sources or food.
• Only a small number of people react to the specific allergen, which is harmless to those who are not allergic to it.
• They may have been in contact with the allergen for years without it causing dermatitis.
• Contact with tiny quantities of an allergen can induce dermatitis.
• Patients with impaired barrier function of the skin are more prone to allergic contact dermatitis, eg patients with leg ulcers, perianal dermatitis, or chronic irritant contact dermatitis.
• Patients with atopic dermatitis associated with defective filaggrin (a structural protein in the stratum corneum) have a high risk of also developing allergic contact dermatitis.

Allergic contact dermatitis has two phases:

1. The sensitization phase in which antigen-specific effector T cells are induced in the draining lymph nodes by antigen captured cutaneous dendritic cells that migrate from the skin.
2. The elicitation phase includes effector T cells that are activated in the skin by antigen captured cutaneous dendritic cells and produce various chemical mediators, which create antigen-specific inflammation.

Both irritant contact dermatitis and allergic contact dermatitis can present with three morphological patterns:

1. Acute phase: erythema, edema, oozing, crusting, tenderness, vesicles or pustules
2. Subacute phase: crusts, scales, and hyperpigmentation
3. Chronic phase: Lichenification.

Hands are the common site of contact allergic dermatitis.

The acute irritant reaction usually reaches its peak quickly, within minutes to few hours after exposure, and then starts to heal, while in allergic contact dermatitis, the elicitation time depends on the characteristics of the sensitizer, the intensity of exposure, and degree of sensitivity. Lesions usually appear 24 to 72 hours after the exposure to the causative agent and reach their peak at approximately 72 to 96 hours. Allergic contact dermatitis improves more slowly than irritant contact dermatitis, and then recurs faster (in a few days) when exposure is re-established.

Allergic contact dermatitis is common in the general population and in specific employment groups.

• It is more common in women than men, mainly due to nickel allergy and, recently, to acrylate allergy associated with nail cosmetics.
• Many young children are also allergic to nickel.
• Contact allergy to topical antibiotics is common in patients over the age of 70 years old.
• Allergic contact dermatitis is especially common in metal workers, hairdressers, beauticians, health care workers, cleaners, painters and florists.

Sometimes it is easy to recognize contact allergy and no specific tests are necessary. Taking a very good history including information on work environment, hobbies, products in use at home and work and sun exposure will enhance the chances of finding a diagnosis. The rash usually (but not always) completely clears up if the allergen is no longer in contact with the skin, but recurs even with slight contact with it again.

The open application test is used to confirm contact allergy to a cosmetic, such as a moisturizer. The product under suspicion is applied several times daily for several days to a small area of sensitive skin. The inner aspect of the upper arm is suitable. Contact allergy is likely if dermatitis arises in the treated area.

Dermatologists will perform patch tests in patients with suspected contact allergy, particularly if the reaction is severe, recurrent or chronic. The tests can identify the specific allergen causing the rash.

Fungal scrapings of skin for microscopy and culture can exclude a fungal infection.

Dimethylgloxime test is available to ‘spot test’ if a product contains nickel.

Active allergic contact dermatitis is usually treated with the following:

• Emollient creams
• Topical steroids
• Topical or oral antibiotics for secondary infection
• Oral steroids, usually short courses, for severe cases
• Phototherapy or photochemotherapy.
• Azathioprine, ciclosporin or other immunosuppressive agent.
• Tacrolimus ointment and pimecrolimus cream are immune modulating drugs that inhibit calcineurin and may prove helpful for allergic contact dermatitis.

Allergic contact dermatitis prognosis

Prognosis depends on patient education and compliance in avoiding allergens and appropriate skin care. Contact allergy often persists lifelong so it is essential to identify the allergen and avoid touching it. Dermatitis may recur on re-exposure to the allergen.

• Some allergens are more difficult to avoid than others, with airborne allergens being a particular problem (eg epoxy resin, compositae pollen).
• The longer a person suffers from severe allergic contact dermatitis, the longer it will take to clear after the diagnosis is made and the cause detected.
• The dermatitis may clear up on avoidance of contact with the allergen, but sometimes it persists indefinitely, eg chromate allergy.

Irritant contact dermatitis causes

Irritant contact dermatitis occurs when chemicals or physical agents damage the surface of the skin faster than the skin can repair the damage. Irritants remove oils and moisture (natural moisturising factor) from its outer layer, allowing chemical irritants to penetrate more deeply and cause further damage by triggering inflammation.

The severity of the dermatitis is highly variable and depends on many factors including:

• Amount and strength of the irritant
• Length and frequency of exposure (eg, short heavy exposure or repeated/prolonged low exposure)
• Skin susceptibility (eg, thick, thin, oily, dry, very fair, previously damaged skin or pre-existing atopic tendency)
• Environmental factors (eg, high or low temperature or humidity).

Irritant contact dermatitis is due to sufficient inflammation arising from the release of proinflammatory cytokines from keratinocytes, usually in response to chemical stimuli. It mainly causes skin barrier disruption, epidermal cellular changes, and cytokine release ¹.

Irritants can be classified as cumulatively toxic (e.g., hand soap causing irritant dermatitis in a hospital employee), subtoxic, degenerative, or toxic (e.g., hydrofluoric acid exposure at a chemical plant) ¹.

Irritant contact dermatitis symptoms

Symptoms of irritant contact dermatitis may include burning, itching, stinging, soreness, and pain, particularly at the beginning of the clinical course. Irritant contact dermatitis is usually confined to the site of contact with the irritant, at least at first. If the dermatitis is prolonged or severe, it may spread later to previously unaffected areas, but it is less likely to do this than allergic contact dermatitis.

Dermatitis often appears as a well-demarcated red patch with a glazed surface, but there may be swelling, blistering and scaling of the damaged area, indistinguishable from other types of dermatitis. It can be very itchy.

Contact irritant dermatitis can appear differently according to the conditions of exposure:

• Accidental exposure to a strong irritant such as a strong acid or alkali substance may cause an immediate skin reaction resulting in pain, swelling and blistering.
• Contact with mild irritants such as water and soap or detergent may over weeks cause dryness, itching and cracking of the skin. Eventually, sores may appear which form crusts and scales.

Some typical examples of irritant contact dermatitis include:

• Dribble rash around the mouth or on the chin in a baby, or older children due to licking; the cause is saliva, which is alkaline. Skin bacteria may contribute to the clinical appearance.
• Napkin dermatitis due to urine and faeces can affect older incontinent patients as well as babies.
• Chemical burns from strong acids (eg, hydrochloric acid) and particularly alkalis (eg, sodium or calcium hydroxide).
• Housewife’s eczema is hand dermatitis caused by excessive exposure to water, soaps, detergents, bleaches and polishes.
• Dermatitis on a finger underneath a ring. Soaps, shampoos, detergents and hand creams may accumulate under the ring and cause irritant contact dermatitis.
• Gloves or glove powder or sweat or tiny quantities of chemicals that have been occluded inside the gloves may have a direct irritant action on hands (rubber may also result in latex or rubber antioxidant allergy).
• Fiberglass may cause direct mechanical/frictional damage.
• Dry cold air may cause dry, irritable skin (winter itch).
• Cosmetics may irritate sensitive facial skin (especially in rosacea) resulting in immediate stinging, burning and redness followed by itching and dryness.
• Gels and solutions tend to be more irritating than creams and ointments.

In time, the skin may develop some tolerance to mild irritants.

Irritant contact dermatitis diagnosis

Patch tests are used to confirm allergic contact dermatitis and identify the allergen(s). They do not exclude irritant contact dermatitis as the two may coexist.

Irritant contact dermatitis treatment

It is essential to recognize how you are in contact with the responsible substance(s) so that, where possible, you can avoid it (them) or at least reduce exposure. Wear suitable gloves to protect against irritants in your home and work environment.

Irritant contact dermatitis is usually treated with the following:

• Chemical burns are usually flushed with water followed by the use of antidote or specific remedy against the particular toxic chemical.
• Friction should be avoided as well as the use of soaps, perfumes, and dyes.
• Compresses, creams and ointments may assist healing
• Active dermatitis is usually treated with the following:
  • Emollient creams are used for hydrating the skin.
  • Topical steroids may be used to reduce the inflammation.
  • Topical or oral antibiotics for secondary infection (usually flucloxacillin or erythromycin).
  • Antihistamines such as hydroxyzine and cetirizine are recommended to control itch (pruritus).
  • Oral steroids, usually short courses, for severe cases but should be tapered gradually to prevent recurrences.

1. Litchman G, Nair PA, Atwater AR. Contact Dermatitis. [Updated 2019 Jun 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459230[↩][↩][↩][↩][↩][↩][↩]
2. Basketter DA, Huggard J, Kimber I. Fragrance inhalation and adverse health effects: The question of causation. Regul. Toxicol. Pharmacol. 2019 Jun;104:151-156.[↩]
3. Bingham LJ, Tam MM, Palmer AM, Cahill JL, Nixon RL. Contact allergy and allergic contact dermatitis caused by lavender: A retrospective study from an Australian clinic. Contact Derm. 2019 Jul;81(1):37-42.[↩]
4. Shane HL, Long CM, Anderson SE. Novel cutaneous mediators of chemical allergy. J Immunotoxicol. 2019 Mar 01;:1-15.[↩]