Eyebrows are the delicate hairs that grow on the brow ridge above the eyes. The purpose of eyebrows is to prevent sweat from getting into the eyes. They also help shield the eyes from sun and keep dandruff and other small particles from falling into the eyes. On average, it takes about six to eight weeks for eyebrows to grow in.
Average Growth Rate
For the average pre-puberty and post-pubescent child, hair grows in at about 0.14 mm each day. For an adult and an elder, hair grows at a rate of about 0.16 mm daily. Eyebrows have the slowest rate of regrowth on the body compared with hair on the scalp and body hair.
Eyebrow hair that is plucked or threaded begins regrowing after about two or three weeks. Plucking involves using tweezers to remove the hair by its root from the hair follicle. Threading involves dragging a piece of cotton thread across the surface of skin and removing hairs in its path. As with tweezing, hairs are removed by the root.
For a post-pubescent or young adult, it takes about 65 days for eyebrows to regrow following plucking. For a mature adult, it will take about 56 days for eyebrow hair to regrow and about 73 days for a person at retirement age. Consistent eyebrow removal can eventually lead to diminished growth, thinning eyebrows and dormant follicles, especially after the age of 42.
Waxing is similar to plucking in that the hairs are removed from the follicle by the root. It takes the same amount of time, about 64 days, for the hairs to grow back. The difference between plucking and waxing is that hairs do not begin regrowing after being waxed for about three to four weeks.
Drugs and Medications
Certain drugs and medications can cause eyebrow hair to fall out. Chemotherapy, which attacks healthy cells, is well known for causing hair loss. Eyebrows can begin growing about one or two months after the completion of chemotherapy. It could take up to six months for eyebrows to fully grow back. It's possible that the new hair will be thinner, a different color or a different texture.
The thyroid plays a major role in hair function, including hair regrowth and hair loss. Hair may begin falling out on the head but can soon spread to the eyebrows. Losing the outer one-third of eyebrow hair is a distinctive symptom of hypothyroidism. Once the underlying condition is treated, and hormone levels in the body are normalized, eyebrows will begin growing back. It can take two or three months for the hairs to fully regrow. However, eyebrows can grow in patchy or only partially.