Reasons for dandruff

Stress
Dry skin
Protein deficiency induced dry scalp
Irritated, oily scalp due to excess production of sebum or oil
Seborrheic dermatitis
Not shampooing often enough leads to accumulation of sebum and dirt on the scalp
Less combing / brushing, as the dead skin flakes are retained on the scalp
Other skin conditions like eczema or psoriasis
A yeast-like fungus called Malassezia
Reaction/ allergy to certain hair care products (contact a dermatologist)
Low immunity
Unhealthy diet, especially due to lack of Vitamin B and Zinc

Seborrheic Dermatitis

One of the major reasons of dandruff, seborrheic dermatitis is an inflammatory skin disorder that affects the scalp, face, and torso. Called cradle cap in infants (which usually goes off by the age of 3), the symptoms of seborrheic dermatitis include red, oily skin, white/ yellow scales and itching.

Medical remedies

Dandruff can be managed with regular use of shampoos containing

Selenium Sulphide
Ketoconazole
Zinc Pyrithione
Salicylic Acid
Coal Tar

Home remedies

Dandruff can also be managed to an extent using home remedies like

Shampoos containing tea-tree oil - A natural antiseptic, antifungal and antibiotic, tea-tree oil, which is obtained from the leaves of Australian tea tree (Melaleuca alternifolia), is a great remedy for dandruff. However, tea-tree oil should be used with care as it may cause allergy in some people.
Massaging the scalp with nutrient rich oils like olive oil and coconut oil to get rid of dryness and itching
Apple cider vinegar helps restore the pH balance of the scalp, and control the growth of yeast. It also helps clean clogged pores and hair follicles.
Aloe vera possesses anti-bacterial and anti-fungal properties that help reduce dandruff
Eat plenty of fruits and vegetables
Drink lots of water
Avoid excess sugar and yeast rich food products
Take selenium, vitamin B, vitamin E, omega-3 fatty acids and zinc supplements, only after seeking advice from your doctor

If dandruff persists, make sure you consult a Dermatologist without delay