Common Scalp Conditions: Contact Dermatitis

Contact dermatitis is an inflammatory skin reaction that develops when the skin comes into contact with a substance that causes irritation or an allergic response. It can affect the scalp and hairline and may sometimes be linked to haircare, styling or cosmetic products.

There are two main types: irritant contact dermatitis and allergic contact dermatitis. Although they can look similar, they develop for different reasons.

Irritant contact dermatitis occurs when a substance directly irritates or damages the skin. This can happen after repeated exposure or following contact with a particularly irritating ingredient.

Allergic contact dermatitis occurs when the immune system develops an allergic reaction to a specific substance. Once sensitised, even relatively small amounts of an allergen can trigger a reaction.

Contact dermatitis affecting the scalp may be particularly relevant where symptoms develop following the use of a new shampoo, conditioner, styling product, treatment or hair colour.

Symptoms can vary depending on the individual and the type of reaction. They may include:

• Itching
• Redness and inflammation
• Burning or stinging
• Dryness or scaling
• Soreness or sensitivity
• Swelling
• Blistering or weeping in more acute reactions
• A rash around the scalp, hairline, ears, neck or face

Allergic contact dermatitis often develops within 24–72 hours of exposure to the responsible allergen, although the timing can vary.

Potential triggers include ingredients found in hair and cosmetic products, including fragrances, preservatives and hair-dye ingredients. Paraphenylenediamine (PPD), used in many permanent hair dyes, is a recognised cause of allergic contact dermatitis. Some preservatives used in hair products can also trigger contact allergy.

Irritant contact dermatitis can develop when the skin barrier is repeatedly exposed to substances that cause irritation. This may be particularly relevant for people who frequently use haircare, styling or chemical treatment products.

Identifying the trigger is an important part of managing contact dermatitis. Where allergic contact dermatitis is suspected, a dermatologist may recommend patch testing, which is considered the standard test for identifying contact allergens.

The most important step in managing contact dermatitis is identifying and avoiding the substance responsible for the reaction. Once the trigger has been removed, the skin can begin to recover. Treatment may also be recommended to reduce inflammation and relieve symptoms, depending on the severity of the reaction. Persistent, recurrent or unexplained symptoms may require assessment by a GP or dermatologist, particularly where allergic contact dermatitis is suspected.

If your scalp becomes persistently itchy, irritated, red or flaky following the use of a hair or scalp product, professional assessment can help identify possible triggers and determine whether further investigation or medical referral is appropriate.