Causes of Contact Dermatitis
Causes of contact dermatitis fall into two main categories: irritant and allergic. Understanding the distinction is essential for identifying the specific triggers and developing an effective treatment plan. Both types result in the same visible symptoms, but the underlying mechanisms differ. Contact dermatitis arises when the skin’s barrier is compromised, either through direct injury or immune system activation.
Irritant Contact Dermatitis
This is the most common type, accounting for around 80% of cases. It occurs when the skin is exposed to substances that directly damage the outer layer of skin cells. These irritants may include:
Soaps, detergents, and shampoos
Solvents like acetone or alcohol
Acids and alkalis
Bleach and disinfectants
Prolonged contact with water
Irritant contact dermatitis tends to affect people in occupations involving frequent hand washing, such as healthcare workers, cleaners, and food handlers. It can occur quickly after a single strong exposure or gradually due to cumulative damage from repeated contact.
Allergic Contact Dermatitis | Causes of Contact Dermatitis
This form results from an immune reaction to a normally harmless substance, referred to as an allergen. Sensitisation usually takes days, weeks, or even months of exposure before symptoms appear. Common allergens include:
Nickel in jewellery or belt buckles
Fragrances and preservatives in cosmetics
Rubber compounds in gloves or shoes
Hair dyes (e.g. paraphenylenediamine or PPD)
Certain plants, such as poison ivy or oak
Once sensitised, even brief exposure to the allergen can trigger a flare-up. The reaction is typically delayed, appearing 24–72 hours after exposure.
Combined Causes | Causes of Contact Dermatitis
In some cases, people may suffer from both irritant and allergic contact dermatitis simultaneously. For example, a weakened skin barrier from repeated hand washing can make someone more susceptible to allergen penetration.
To summarise, causes of contact dermatitis involve either direct damage from irritants or immune response to allergens. Identifying the specific cause is essential to eliminate exposure and tailor treatment, especially for individuals with occupational risks or chronic skin conditions.
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