stress

This is correct on a number of counts. Firstly, stress can accelerate hair loss. Hormones released in your body cause hair follicles to stop growing new hair during these times, so when hair falls out as normal, there is nothing there to replace it.

Stress can also contribute to the onset of dandruff. It causes accelerated production of a scalp yeast, irritating the scalp, which in turn produces more cells, so the dead cells come loose (flakes). The stress of having dandruff could make this a vicious cycle, so the best thing you can do is take a deep breath, count to 10, and keep your hair on. Literally.