It is not recommended ,to pluck facial hair, especially on hormonally driven areas e.g upper lip and chin. Waxing and tweezing can make it worse. Anytime you rip a hair from the follicle , blood rushes to the area. Blood supply is what nourishes the dermal papila of a hair to grow.So you are encouraging healthier hair to return in place of the one you just removed. Also blood affects the surrounding tissue as well, so it can stimulate nearby follicle to grow hairs.