Hair grows from follicles, which are tiny pockets in the skin. The hair shaft emerges from the follicle and grows outward. There's no space for hair to grow inward or under itself.
It sounds like you might be thinking about something else. Perhaps you're thinking about how long hair can get tangled, or how it can become matted if it isn't properly cared for.
Could you tell me more about what you're thinking? Maybe I can help you understand better.