As a biologist with a focus on cellular biology, I can explain the process of hair growth and why it grows back after being cut. Hair growth occurs in cycles, which include the anagen (growth), catagen (transitional), and telogen (resting) phases. When you cut your hair, you're only cutting the hair shaft, which is the visible part of the hair that extends above the skin's surface. The hair follicle, which is the part of the hair that produces the hair shaft, remains intact beneath the skin.

The hair follicle is a complex structure that contains cells that are continuously dividing and producing new hair. Even when you cut your hair, these cells continue to divide and push the new cells up the follicle, which causes the hair to grow longer. The rate of growth is determined by a combination of genetic, hormonal, and nutritional factors.

Here's the translation in Chinese:

作为一位专注于细胞生物学的生物学家，我可以解释头发生长的过程以及为什么剪掉后会重新生长。头发生长是周期性的，包括生长期（anagen）、退行期（catagen）和休止期（telogen）。当你剪头发时，你只是剪掉了头发干，这是头发可见的部分，它延伸在皮肤表面之上。而毛囊，即生产头发干的部分，在皮肤下面保持完好。

毛囊是一个复杂的结构，包含不断分裂并产生新头发的细胞。即使你剪了头发，这些细胞仍然继续分裂并将新细胞向上推至毛囊，这导致头发变得更长。生长速度由遗传、激素和营养因素共同决定。

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Cutting the ends of your hair doesn't affect the follicles in your scalp, which determine how fast and how much your hair grows, says Paradi Mirmirani, MD, assistant professor of dermatology at the University of California, San Francisco. Hair grows an average of a quarter-inch every month��whether or not you cut it.read more >>