Dandruff and seborrheic dermatitis are often mentioned together. Dandruff is the mildest manifestation of seborrheic dermatitis and it cannot be separated from seborrheic dermatitis.Therefore, what is mentioned in the article for seborrheic dermatitis is also true for dandruff and vice versa.
Dandruff is also known as scurf - its medical term is Pityriasis capitis.

Dandruff is normal shedding of skin. On most of the body surface, the flakes of dead skin fall on the shoulders from the head and troubles the skin of the face and back also without notice, but they can accumulate in the hair especially when you scratch your head, brush your hair, or pull a shirt over your head.
Sometimes, during puberty, your oil glands go toward a little wild, and you develop a lot more dandruff than normal.
People who suffer from dandruff problem are prone to get acne, pimples and boils on the face and back due its fall on these parts. Dry, thick lesions consisting of large, silvery scales may be traced to the less common psoriasis of the scalp.
Seborrheic dermatitis in children and infants, also called cradle cap, is a harmless, temporary condition. It appears as thick, crusty, yellow or brown scales over the child's scalp appearing in the first 12 weeks of life.

Dandruff is mainly caused due to a fungus called Malassezia furfur (or also known as Pityrosporum). This is generally and naturally found on the skin surface of all people. The bad news that Malassezia furfur not affected by UVA light.
Dandruff can be caused or exacerbated by hormonal imbalances, poor general health, or a hereditary predisposition, and your doctor can help you find ways to approach these issues.
Dandruff can also be caused by frequent exposure to extreme heat and cold. As it is normal for skin cells to die and flake off, a small amount of flaking is normal and in fact quite common.

  Dandruff is characterized by grayish-white flakes or scales on the scalp   and an itchy scalp as a result of excessive scaling. In dandruff the epidermal cell turnover is at twice the rate of those without the condition.

In Seborrheic dermatitis you can determine red scaly lesions mostly found on the scalp, and upper trunk. The skin lesions are distributed on the scalp, eyebrows, nasolabial folds, cheeks, ears, presternal and interscapular regions, axillae, and groin.

In psoriasis Dandruff

  the scales are silvery-white and associated with red, patchy plaques and inflammation.

  In dandruff the scalp is the only area affected. More widespread seborrhoeic dermatitis affects the areas where there is greatest sebaceous gland activity, so it can affect eyebrows, eyelashes, moustache,  paranasal clefts, behind the ears, nape of neck, forehead and chest.

    Psoriasis Dandruff can affect the scalp but other areas are involved. The knees and elbows are commonly involved but the face is rarely affected. This latter point distinguishes psoriasis from seborrhoeic dermatitis, where the face is often affected.

Severity

  Dandruff is generally a mild condition. However, the itching scalp may lead to scratching, which may break the skin, causing soreness and the possibility of infection.

Previous history

  Since dandruff is a chronic relapsing condition there will usually be a previous history of fluctuating symptoms. There is a seasonal variation in symptoms, which generally improve in summer in response to UVB light. Malassezia furfur is unaffected by UVA light.

Aggravating factors

  Hair dyes and perms can irritate the scalp. Inadequate rinsing after shampooing the hair can leave traces of shampoo causing irritation and itching.

The aim of treatment is to reduce the level of Malassezia furfur on the scalp; therefore agents with antifungal action are effective. Ketoconazole, selenium sulphide, zinc pyrithione and coal tar are effective.
Ketoconazole is the most and coal tar is the least effective. All treatments need to be left on the scalp for 3-5min for full effect.

Ketoconazole "Nizoral"
Ketoconazole is the best dandruff shampoo there is good evidence of effectiveness of ketoconazole in the treatment of dandruff. The formulation available is ketoconazole 2% shampoo. The treatment should be used twice a week for 2-4 weeks
It can control dandruff flaking while leaving hair clean, shining and easy to manage. It is the dandruff shampoo you can make your regular shampoo.
Ketoconazole is not absorbed through the scalp and side-effects are to some extent rare.

Selenium sulphide 2.5%
Selenium sulphide has been shown to be effective and works by reducing the cell turnover rate (cytostatic effect).
Twice-weekly use for the first 2 weeks is followed by weekly use for the next 2 weeks; then it can be used as needed. The hair and scalp should be thoroughly rinsed after using selenium sulphide shampoo, otherwise discoloration of blond, grey or dyed hair can result.
Frequent use can make the scalp greasy and therefore exacerbate seborrhoeic dermatitis. Products containing selenium sulphide should not be used within 48h of coloring or perming the hair.
Selenium sulphide should not be applied to inflamed or broken skin.

Zinc pyrithione
Shampoos containing zinc pyrithione are general sales list (GSL) products and are generally considered as cosmetics. It reduces the fungus that causes dandruff. Zinc pyrithione effective against dandruff and has a cytostatic effect. It should be used twice weekly for the first 2 weeks and then once weekly as required.

Coal tar "Coral Tree stem bark extracts"
Coal tar can help dandruff conditions by slowing skin cell turnover. Modern formulations are pleasanter than the traditional ones but some people still find the smell of coal tar unacceptable. Coal Tar is devoid of the side effects like loss of taste, gastric irritation and hepato-toxity which is common with conventional AntiFungals. However, it can cause skin sensitization and is a photosensitize.

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