You can tolerate or despise them, but menstrual cycles are a fact of life many of us have to deal with, either way. And while it's easy to think of PMS and periods as things that happen to our bodies every few weeks, the truth is that we are constantly in hormonal flux — thus, affected inside and outside, head-to-toe throughout the month.We recently wrote about the menstrual cycle and skin , and now we're taking it a step further and discussing how your period can affect your hair. "Although we mostly think of skin as being most reactive to the hormonal, and other, changes of the menstrual cycle, the fluctuations of the menstrual cycle can, in some cases, directly and indirectly affect the scalp and hair," explains dermatologist Sophia Kogan , MD, of Nutrafol.To ensure your hair looks and feels its best no matter the time of the month, we're breaking things down based on your period cycle. Ahead, see when it's best to color your hair, when you should wash it more often, and when you can go more days depending on dry shampoo.Note: If you're taking any hormonal birth control, your hormones are regulated and ovulation doesn't occur. For that reason, you may not notice the same hormonal fluctuations and hair or scalp changes as you would sans pill or other birth control.You probably look and feel your best in the final days of your period, and in the week or so following. During this portion of your cycle, your estrogen levels begin to increase and testosterone, responsible for triggering oil production, decreases, says Dr. Kogan.This may be great news for your skin, because you'll experience less sebum buildup and a clearer complexion. But a reduction in oil on your scalp can lead to an overall drier head of hair. While imperceptible to some, this reduction is especially noticeable if you already struggle with dryness."If [your hair is normally dry], you may need to condition more in the post-menses phase, and possibly the latter part of the menses, before the oil production kicks up," advises Sejal Shah , MD, a dermatologic surgeon who works with RealSelf.com Whether you have a normal, oily, or dry scalp, though, this is the ideal time of the month to do your deep-conditioning. You may also find that you need to wash your hair less due to decreased oil production. If you want to extend your time between shampooing, but want to maintain shine and vibrancy, use hair serum on your ends and dry conditioner anywhere it's needed.About 14 days before your period begins, and a week before all those dreaded PMS effects kick in, an egg starts making its way out of your ovary and through your fallopian tube to check into the ol' uterus hotel. As this happens, your body begins producing even more estrogen, which triggers the production of LH, also known as luteinizing hormone . This hormone is responsible for a slight increase in oil production.This slight increase is actually a good thing for your hair and scalp, which were experiencing dryness the week before. The high estrogen levels and low testosterone levels keep oil production in check to prevent excess sebum. You're still getting a little extra oil, though, thanks to LH, explains Dr. Shah. Which means your scalp and hair should look and feel pretty damn good.You can continue washing and conditioning as normal, but do use a gentle hand since your senses — including touch — are heightened during this time period. Intensive scrubbing can leave your scalp feeling overworked.