Dandruff can be caused by too strong hair detergents, styling agents, stress, poor diet, too dry scalp or, for example, inflammation of the scalp, i.e. sebaceous dermatitis.
Dandruff on a dry scalp is often a fine and dusty white scale, while dandruff on an oily scalp is a larger, yellowish scale.
Dandruff is often caused by the wrong type or too strong hair products, such as shampoos containing strong sulfates or styling products that are too strong. Sulfates (SLS, i.e. Sodium Lauryl Sulfate) are cheap foaming cleansers that are very powerful, good grease removers.
Chemically, sulfate is a long-chain alcohol and drying agent that leaves the scalp damaged and more susceptible to scalp infections. So the annoying little light flakes on your shirt are most likely caused by the wrong kind of shampoo.
Most of the time the treatment of a flaky scalp can be done with home remedies by switching to a shampoo that does not contain sulfates. All shampoos in Saari Taia's selection are sulfate-free and gentle.