Folliculitis is inflammation of the hair follicle. Sometimes bacteria is involved, which can lead to infection.
It is not the same as an ingrown hair, but they can be connected. An ingrown hair can irritate the follicle and lead to folliculitis, but it can also happen on its own.
After laser hair removal, the follicle has been heated and is more sensitive. Heat, sweat, friction, or bacteria can trigger a reaction, which is why folliculitis develops later rather than during treatment.