Contact dermatitis
Contact dermatitis is a reaction that happens after your skin comes in contact with certain substances.
Skin irritants cause most contact dermatitis reactions. Other cases are caused by allergens, which trigger an allergic response. The reaction may not start until 24 to 48 hours after exposure. Contact dermatitis, caused by an irritant that is not an allergic response, happens from direct contact with the irritant.
In this article:
- What is contact dermatitis?
- Types of contact dermatitis
- Allergic contact dermatitis
- Irritant contact dermatitis
- Symptoms
- When to see a doctor
- What causes allergic contact dermatitis?
- What causes irritant contact dermatitis?
- Risk factors
- Complications
What is contact dermatitis?
Contact dermatitis is a reaction that happens after your skin comes in contact with certain substances.
Skin irritants cause most contact dermatitis reactions. Other cases are caused by allergens, which trigger an allergic response. The reaction may not start until 24 to 48 hours after exposure. Contact dermatitis, caused by an irritant that is not an allergic response, happens from direct contact with the irritant.
Allergic contact dermatitis most commonly affects adults, but it can affect people of all ages.
Types of contact dermatitis
While the contact dermatitis is the general name for rashes caused by some substances, the condition is still divided based on the mechanism of the reaction:
- Allergic contact dermatitis
- Irritant contact dermatitis
Allergic contact dermatitis
Allergic contact dermatitis is caused by your body’s reaction to something that directly contacts the skin. Many different substances can cause allergic contact dermatitis, which are called ‘allergens’. An example of this is poison ivy or nickel. Usually these substances cause no trouble for most people, and may not even be noticed the first time the person is exposed. But once the skin becomes sensitive or allergic to the substance, any exposure will produce a rash.
The rash usually doesn’t start until a day or two later, but can start a soon as hours or as late as a week. A feature unique to allergic contact dermatitis is that the rash is not always localized to the area of contact with the substance and a rash can appear on other areas of the body. Allergic contact dermatitis is not usually caused by things like acid, alkali, solvent, strong soap or detergent.
Irritant contact dermatitis
Occupational irritant contact dermatitis is an inflammation caused by substances found in the workplace that come in direct contact with the skin. Signs of irritant contact dermatitis include redness of the skin, blisters, scales or crusts. These symptoms do not necessarily occur at the same time or in all cases.
This kind of dermatitis is caused by chemicals that are irritating (e.g., acids, bases, fat-dissolving solvents) to the skin and is localized to the area of contact. The most common location affected by occupational contact dermatitis is the hands.
While people who work with chemicals are easy to diagnose due to nature of the exposure, it is much more difficult to suspect the contact dermatitis that happens at home due to use of household cleaning materials. It is also extremely hard to track down the product that causes the reaction, as the symptoms are not immediate (can start happening 2-3 month after the product use). Also, as the cleaning product have been used on multiple surfaces, you would not even know that the rash on your hands is from touching a dining table cleaned with a wood treatment oil.
Symptoms
Contact dermatitis usually occurs on areas of your body that have been directly exposed to the reaction-causing substance — for example, along a calf that brushed against poison ivy or under a watchband. The rash usually develops within minutes to hours of exposure (if you are sensitized). If this is your first reaction, it can take 12-24 hours, and it can last two to four weeks.
The rash may appear similar to many other forms of dermatitis and may ve confused for other common rashes such as eczema. The first redness and blisters usually take a shape of the area you have touched
Allergic contact dermatitis symptoms associated with allergic contact dermatitis include:
- dry, scaly, flaky skin
- hives
- oozing blisters
- skin redness
- skin that appears darkened or leathery
- skin that burns
- extreme itching
- sun sensitivity
- swelling, especially in the eyes, face, or groin areas
Irritant contact dermatitis may cause symptoms, such as:
- blistering
- cracking skin due to extreme dryness
- swelling
- skin that feels stiff or tight
- open sores that form crusts
When to see a doctor
See your doctor if:
- The rash is so uncomfortable that you are losing sleep or are distracted from your daily activities
- The rash is spreading, painful, severe or in the hard to treat areas
- You’re embarrassed by the way your skin looks
- The rash doesn’t get better within two-three weeks
- The rash affects your face or genitals
Seek immediate medical care in the following situations:
- You think your whole skin is infected (systemic reaction). Clues include fever and pus oozing from blisters.
- Your lungs, eyes or nasal passages are painful and inflamed, perhaps from inhaling an allergen.
- You think the rash has spread to the mucous lining of your mouth and digestive tract.
What causes allergic contact dermatitis?
Allergic contact dermatitis is a type 4 or delayed hypersensitivity reaction and occurs 48–72 hours after exposure to the allergen. Allergy does not develop from the first exposure, or the symptoms may be very mild. This is called sensitization. Next time, when you touch the same substance, like poison oak leaf, your immune system will remember it and attach it at full force. The reaction may become systemic, meaning the rash will spread over the whole body, even if you touched the oil only in one spot.
The mechanism involves immune cells, which recognise an antigen on the skin surface, releasing active biological factors that activate the immune system. As a result, the skin cells become damaged and nerve ending transmit the signal of “itch” to the brain. The liquid which normally is under the skin, starts coming out and forms blisters and oozing.
Things to remember:
- 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.
What causes irritant contact dermatitis?
Irritant contact dermatitis develops when chemical or physical agents damage the skin surface faster than the skin can repair. Irritants remove oils and natural moisturizing factor from the outer layer of the skin, allowing chemical irritants to penetrate the skin barrier and trigger inflammation.
Factors influencing the development and severity of the dermatitis include:
- Concentration, amount, and properties of the irritant
- Duration and frequency of exposure, for example short concentrated or repeated prolonged low exposure
- Skin susceptibility such as pre-existing skin damage or atopic tendency
- Mechanical trauma including hand scrubbing
- Environmental factors such as temperature extremes or humidity.
Everyday examples of common skin irritants are water, soaps, and, in the era of COVID-19, hand sanitizers. Occupational irritants can include wet work, detergents, solvents, acids, alkalis, adhesives, and metalworking fluids.
Topical medications such as retinoid and benzoyl peroxide, may cause irritant contact dermatitis with long-term use. Friction, sweating, and heat are examples of environmental factors. Irritant dermatitis is often the result of the cumulative impact of multiple irritants.
Risk factors
Some jobs and hobbies put you at higher risk of contact dermatitis. Examples include:
- Health care and dental employees
- Metalworkers
- Construction workers
- Hairdressers and cosmetologists
- Auto mechanics
- Scuba divers or swimmers, due to the rubber in face masks or goggles
- Cleaners
- Gardeners and agricultural workers
- Cooks and others who work with food
Complications
Contact dermatitis can lead to an infection if you repeatedly scratch the affected area, causing it to become wet and oozing. This creates a good place for bacteria or fungi to grow and may cause an infection.
If you are not careful and scratch the rash, it can cause permanent scars and depigmentation. Also, steroid creams can make skin thinner and lighter in color. This changes can be avoided by following doctor’s instructions on skin care, and not overusing over-the-counter steroidal creams.
The rash itself is ugly, and can cause significant anxiety or depression, if present for a while with no resolution. As this is totally treatable condition, it is important to see a specialist who can diagnose correctly and give you avoidance guidance. Sometimes, you will need special accommodations at work, or to think about changing your soaps and cleaning materials at home.
