Why does hair thicken and become more rough after a razor shave but not after one using a trimmer? If a razor cuts only the hair, then how does hair thicken and become more rough with a razor shave and not after one using a trimmer? If both are used for hair removal, why is there a difference in hair growth? I have been using a trimmer for 1 year, but the growth of hair remained unchanged. When I started shaving with a razor, the hair growth thickened.

Hair does not grow back thicker when it is cut. This is somewhat of an optical illusion because when you shave with a razor it leaves the top of the hair flat rather than pointed so it appears thicker. For instance see this picture:

!Hair being cut

As you can see the hair is tapered at the top and when cut loses this taper to leave a large cross-sectional area. I would say that for your question with with the trimmer that it is probably cutting the hair further up the taper where the hair is 'thinner' to begin with. A razor cuts closer to the base and thus gives a thicker appearance.

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