The naturally occurring microbe, Malassezia Globosa is found on everyone’s scalp. It feeds on the natural oils (sebum) in the scalp; sebum is present to keep your hair and the skin on your scalp well-moisturised. As the sebum breaks down, it produces a by-product known as oleic acid. It is estimated that fifty percent of people are sensitive to oleic acid, so their scalp responds by becoming irritated and inflamed. This inflammation causes the scalp to become red and itchy, leading the body to signal to the brain to shed skin cells at a faster rate. This shedding is an attempt to get rid of the irritant, and physically appears as visible white flakes that often fall onto your shoulders.

A lot of people think dandruff is a product of poor hygiene. But nothing can be further from the truth. Here are few factors that cause dandruff :

• Hormone Imbalance – Hormones play a key role in our body’s oil production. Excess oil in our body triggers the growth of Malassezia globosa, the dandruff causing fungus.
• Harsh Hair Products – Hair care products, especially those containing harsh, synthetic chemicals and toxic ingredients, can rob the scalp of its natural pH, dehydrating it.
• Alcohol Consumption – Alcohol is a well known diuretic which dehydrates the skin.
• Nutrient Deficiency – Research has shown that individuals who rarely consume foods rich in vitamin B12, vitamin E, zinc and essential fatty acids are more prone to dandruff than those who at a balanced diet.
• Stress – When we are stressed, we trigger production of certain hormones, which causes over production of sebum on the scalp.
• Weather Extremes – Extreme weather conditions can either strip the scalp of its natural oils, or cause an overproduction of sebum.

Reference : https://www.simplyorganicbeauty.com/wp-content/uploads/2018/01/Dandruff-Causes.jpg