Q: What does the hair transplantation process do to your existing hair? — R.V., London, UK

A: When we perform hair transplant surgery, we transplant into an area that is either bald or has some existing hair. The hair that is existing is undergoing a process called miniaturization. What this means is that the hairs are continuing to decrease in size – both in diameter and in length. When we perform a hair transplant, we don’t transplant around the existing miniaturized hair on your scalp, we transplant through it. And the reason why we do that is because the miniaturized hair, the fine hair that is being affected by DHT, is eventually going to disappear, so you don’t want there to be any gaps.

So the question is, does the hair transplant actually destroy the existing hair? The answer is that it doesn’t destroy, but it can “shock” it. In other words, creating recipient sites (that the grafts are placed into) will temporarily alter the local circulation of the scalp and this can cause some of the hair in the area to be shed. The reason why hair may be shed is that hair is naturally cyclical. In other words, hair is normally growing, shedding, and then regrowing again. When you stress the scalp, the growing hair may be shed prematurely, but then it regrows.

If you think about the process of electrolysis, it makes sense that you don’t damage follicles from making recipient sites during a hair transplant procedure. In electrolysis used to treat unwanted hair, you stick a needle in the follicle, and you turn on an electric current. And you burn it. And then what happens to the hair? It usually comes back and you need to do it a few more times, even though we are applying an electric current via a needle placed directly in the follicle. So it makes sense that by just inserting a fine needle – the tool commonly used to make a hair transplant site – into the skin, one would not destroy hair follicles. However, the cumulative effect of making hundreds or thousands of recipient sites does shock the follicles and, as a result, some may shed their hair.

It can occur with general anesthesia – when the scalp is not even touched – and it can occur with oral medications, from pregnancy, or after psychological stress. So if you have hair restoration surgery and there is shedding, and it takes six months to a year for the transplanted hair to grow in, during this time hair transplant patient will experience some thinning. Since miniaturized hair is going to eventually disappear anyway, some of the miniaturized hair that is shed may not return. But if it is healthy hair, and it is shed, it will grow back. And, of course, the transplanted hair will be growing in as well during this time.

I am often asked to describe how much can be expected to be shed. The answer is that it is an amount that is often noticeable by the patient, but not noticeable by anyone else.

• Read about the hair transplant procedure