Have you ever wondered why your hair grows faster on one side than the other? And, no matter how many times you cut it to even it out, that one side always grows longer.  And, guess what. Your fingernails and toenails may grow faster on one side of your body than the other, too. What’s going on? Science may offer some answers.

Factors That Affect How Fast Hair Grows

Nutrition, stress, exercise, and medications all affect how quickly your hair and nails grow. You might think nutrients get distributed uniformly throughout your body, but that’s not really the case. Each hair follicle and nail has its own blood supply. The blood supply may be slightly asymmetrical, which is one of the reasons blood pressure may vary slightly when measured from one arm versus the other. If one follicle gets more blood than another, it gets more glucose, hormones, oxygen, and other nutrients. Carbon dioxide and other wastes are carried away more efficiently. Under ideal conditions, improved circulation causes hair to grow more quickly. Also, medications and hormones may negatively impact circulation slowing hair growth noticeably on one side before the other.

To some extent, a person’s circulatory system is genetic. So, you might see hair growing more quickly on one side than the other in a family. Much of the time, the growth difference is caused by behavior. Factors under your control that affect growth rate include:

• Whether you sleep on your back or favor one side or the other. Blood vessels may be compressed at night, leading to an observable growth difference.
• How you style your hair. If you pull it to the side, one side may be more protected than the other. If you always brush your hair the same way, it could stress hair on one side more than on the other.
• Whether you are right-handed or left-handed. This affects how you brush your hair and how you shave. Because each hand serves somewhat different purposes in the course of your day, one may get more exercise and circulation than the other.
• Your habits. Do you drum the nails from one hand more than the other? Do you twist your hair when bored or nervous?
• How much you drive. If you drive a car a lot, one side of your body gets exposed to a lot more solar radiation than the other. Light affects biochemical processes.

It’s Not the Same for Everyone

Human circulation is asymmetrical to begin with, yet you'll find people with faster growth on the right side and others with quicker growth on the left side. In some persons,, there may be no noticeable difference between one side or the other. 

Scientists have found hair generally grows faster at the front of the head than at the back. Age and hormones play a role in hair growth rate, as well as color and texture. The natural color of your hair even affects its growth rate, as gray hair grows at a different rate than pigmented hair.

Does your hair grow faster on one side than the other or is this something you’ve never thought about before?

References

• Bernard, Bruno A. (2016) Advances in Understanding Hair Growth. F1000 Faculty Rev-147. doi: 10.12688/f1000research.7520.1
• Hayashi S., Miyamoto I., Takeda K. (1991) Measurement of human hair growth by optical microscopy and image analysis. Br J Dermatol. 125(2):123-9.
• Van Neste, D. (2004) Thickness, medullation and growth rate of female scalp hair are subject to significant variation according to pigmentation and scalp location during ageing. Eur J Dermatol. 14(1):28-32.