My 13-year-old daughter has really bad dandruff and although she's been using an anti-dandruff shampoo, it just won't go away.

She's also suffered from allergies since she was a toddler, and often gets itchy rashes in the crook of the arms and at the back of her knees. What can she do?

Most dandruff is due to a disease called seborrheic dermatitis and yeast of the Malassezia genus, as well as genetics, stress, and environmental factors contributing to the pathogenesis of this condition. Severe dandruff does not respond well to a single therapy.

Various medicated or anti-fungal shampoos (ketoconazole, ciclopirox), as well as zinc pyrithione and tar-containing shampoo can be used in combination for good results. You can also apply mineral oil or olive oil, leave it overnight and wash it off in the morning.

If that doesn't help, ask your doctor to prescribe a steroid lotion to reduce the inflammation of the scalp.

Dry itchy rashes in the folds of the arms and the back of the knees are commonly caused by a chronic condition called atopic dermatitis.

Proper skin care plays a large role in its treatment. Start with applying a fragrance-free moisturiser right after showering, use only mild soap and keep the water temperature cool. Avoid contact with anything that irritates the skin such as detergents, solvents, harsh soap, and synthetic fibres.

Certain foods such as are peanuts, eggs, milk, salt-water fish, wheat, and soy can exacerbate the rash in some patients. If food allergy is suspected, keep a food diary.

For specific treatments, corticosteroid creams, anti-histamine, or an immune system modulating drug can be used to reduce the inflammation and the itch.

As a number of skin conditions can resemble atopic dermatitis, consult a dermatologist for accurate diagnosis and treatment.

Thidakarn Ratanabanangkoon, MD, anti-ageing physician and dermatologist at Samitivej Srinakarin Hospital's Esthetics Institute.