Scalp Rash: What Is Causing It?

Common causes of a scalp rash

Seborrheic dermatitis

Seborrheic dermatitis is the most common scalp rash in adults. It is an inflammatory reaction linked to a yeast (Malassezia) that lives on oily skin.

• Greasy, yellowish or white flakes on a pink or red base
• Itching, worse in winter and with stress
• Often also affects the eyebrows, sides of the nose, behind the ears and the center of the chest
• Mild forms are plain dandruff

In babies it appears as cradle cap: thick, yellow, crusty scales that are harmless and usually clear by 6 to 12 months.

Scalp psoriasis

Psoriasis affects the scalp in about half of people who have it.

• Thick, well-defined, red plaques with silvery-white scale
• Often extends beyond the hairline onto the forehead, neck and behind the ears
• Can be very itchy and may bleed when scratched
• Patches on elbows, knees, nails or the lower back support the diagnosis

Contact dermatitis

An allergic or irritant reaction to something applied to the scalp. Hair dyes containing PPD (para-phenylenediamine) are a classic trigger, along with fragrances, preservatives, bleaching agents and relaxers. See contact dermatitis.

• Itching, burning, redness and sometimes blisters and oozing
• Often worse at the hairline, ears, eyelids and neck, where the skin is thinner
• Starts hours to 2 days after exposure

Folliculitis

Folliculitis is inflammation of hair follicles, often from bacteria or yeast. It causes small, itchy or tender red pimples or pustules centered on hairs, often at the back of the scalp and hairline. Shaving, tight hairstyles, sweating and hot tubs make it more likely.

Ringworm of the scalp (tinea capitis)

Tinea capitis is a fungal infection that mainly affects children aged 3 to 10.

• Round, scaly patches with hair loss
• Broken hairs that look like black dots
• Swollen glands at the back of the neck
• Sometimes a boggy, painful swelling with pus (kerion), which can scar if not treated

It needs antifungal tablets, because creams cannot reach deep into the hair follicle.

Head lice

Head lice cause intense itching, especially behind the ears and at the nape of the neck. Scratching leaves small red bumps and scratch marks. You may see lice or nits (eggs) stuck firmly to hairs close to the scalp.

Less common causes

• Shingles: a painful band of blisters on one side of the scalp or forehead
• Lichen planopilaris and discoid lupus: inflamed, scaly patches that cause permanent scarring hair loss
• Dermatomyositis: a scaly, itchy, purplish scalp rash with muscle weakness
• Skin cancers: actinic keratoses and basal or squamous cell cancers on sun-exposed bald scalp
• Atopic eczema in people with eczema elsewhere

How to tell scalp rashes apart

How a doctor diagnoses a scalp rash

Most scalp rashes are diagnosed by looking at the scalp and other skin areas. A doctor may use a dermatoscope (magnifier), scrape scales or pluck hairs to test for fungus, take a swab from pustules, or perform a small biopsy for scarring or unusual rashes. Patch testing identifies the cause of contact allergy.

Scalp rash treatment

Seborrheic dermatitis and dandruff

• Medicated shampoos used 2 to 3 times a week, left on for 5 minutes: ketoconazole, selenium sulfide, zinc pyrithione or coal tar
• Rotate shampoos if one stops working
• Short courses of steroid lotions or foams for flares, on a doctor's advice

Scalp psoriasis

• Salicylic acid or coal tar shampoos to soften and lift scale
• Prescription steroid or vitamin D (calcipotriene) lotions, foams or gels
• Phototherapy, or tablets and biologic injections for severe or widespread psoriasis

Contact dermatitis

• Stop the product, rinse thoroughly, and avoid it in the future
• Steroid lotions for inflammation. Severe reactions may need steroid tablets
• If you are allergic to PPD, check labels and ask stylists about alternatives. "Natural" black henna often contains PPD

Folliculitis

Antibacterial washes, warm compresses, and antibiotic or antifungal treatment depending on the cause. Avoid shaving the area while it heals.

Tinea capitis

Antifungal tablets such as griseofulvin or terbinafine for 4 to 8 weeks, plus an antifungal shampoo for the child and household members to reduce spread. Children can usually attend school once treatment starts.

Head lice

Over-the-counter lice treatments, following the label exactly, and repeated as directed, plus wet combing with a fine-toothed nit comb. Check all household members.

Frequently asked questions

What causes a rash on the scalp?

The commonest causes are seborrheic dermatitis, psoriasis, allergic reactions to hair products or dyes, folliculitis, fungal ringworm in children and head lice. Less common causes include shingles, lupus and other scarring conditions that can cause permanent hair loss.

What does a seborrheic dermatitis scalp rash look like?

It looks like greasy, yellowish or white flakes on pink or red skin, often itchy. It may also affect the eyebrows, the sides of the nose and behind the ears. It tends to flare in winter and with stress, and improves with antifungal shampoos.

How do I know if my scalp rash is psoriasis?

Psoriasis plaques are thicker, redder and more sharply outlined than seborrheic dermatitis, with silvery scale, and often extend past the hairline. Psoriasis on the elbows, knees or nails, or a family history, makes it more likely. A dermatologist can confirm it.

Can hair dye cause a scalp rash?

Yes. PPD in permanent hair dyes is a common cause of allergic contact dermatitis, causing itching, redness, swelling and oozing on the scalp, face and neck. Severe swelling of the face or breathing difficulty is an emergency. Do a patch test 48 hours before each dye use.

When should I see a doctor for a scalp rash?

See a doctor if the rash causes hair loss, has pus or painful swelling, comes with fever, follows a severe reaction to a product, or has not improved after 4 weeks of over-the-counter treatment. Children with scaly patches and hair loss need antifungal tablets.