Many nail biters wonder how long it will take until their fingernails have fully grown out and returned to their “normal” shape. To answer the question, let’s first examine how exactly fingernails grow.
Fingernails are composed of protein fibers called "keratin" which is the same protein hair is made of. Growth occurs from the moon shaped area seen at the base of the nail, the so-called "lunula". As new cells grow, the older cells harden and push outward—creating the nail plate, the actual fingernail, which is made of about 150 densely packed layers of protein.
So how fast do the nails grow?
On average, the fingernails grow 1mm per week, while this number may vary slightly due to factors such as age, weather, health and diet. A good estimate would be that it takes about 3-5 weeks for the nails to fully grow out depending on the degree to which you bite your nails. Many nail biters observe that their nails grow faster than normal. This notion is supported by a clinical study done in 1980 y W.B. Bean (a practicing medical professional). He observed nail growth patterns over many years and noticed that the growth of nail biters' nails was accelerated by as much as 20%! The reasoning behind it being that nail biting increases blood flow to the fingertips, thus speeding up nail growth.
After the nails have reached the edge of your fingertips, it will take an additional 2-4 months until they have returned to their prior, normal appearance.
This is due to the fact that nail biting changes the shape of the nail bed: As you chew off nail corners and tear off skin from the nail bed, the width of the nail decreases and the nail bed starts to shorten, possibly interfering with nail growth and leading to irregularities or, in some cases, color changes.
Long-term cuticle pickers may also notice that calluses have developed around the sides and tips of their nails, blocking further outside growth and making it all the more difficult for the nail beds to go back to their original shape.
Taking these factors into consideration, be prepared for it to take 3-4 months for the "final marks of abuse" to truly be behind you. The pride and confidence that will come from your new-grown, beautiful nails will more than make up for your effort and patience.