Noncicatricial alopecia is when a person's hair falls out, but the skin on their head stays normal and healthy. Imagine your hair is like a garden, and the hair follicles (little pockets where hair grows from) are like the seeds. Sometimes the hair follicles stop producing hair, and this can happen for many reasons. It could be because of stress, hormones, certain medicines, or just because a person's body isn't making hair right.
This kind of hair loss is different from another kind called cicatricial alopecia, which is like when your garden gets damaged and can't grow anything anymore. With noncicatricial alopecia, the follicles can still grow hair again if the problem is fixed. That's why it's important for people to go to the doctor if they notice they are losing a lot of hair, so they can find out what the problem is and try to fix it.