Boils are most commonly caused by staph infections - infections by the staphylococcus aureus bacteria. These bacteria are normally found on the skin, but in some cases, such as when shaving, the bacteria find their way into the skin, where they infect the hair follicles and as a result cause boils. Boils are usually quite harmless, although they are often painful and unpleasant to look at. In some cases, they can worsen to the point where they turn into abscesses, which are similar but larger and more serious. Usually however, a boil will take its own course and disappear within approximately a week.
I am not aware of any reason why your menstrual period should result in the appearance of boils. As mentioned earlier, boils are the result of bacterial infections, and have nothing to do with hormonal fluctuations and the menstrual process.
Perhaps there is some indirect connection between the start of your menstrual period and the appearance of the boils. There are probably several changes in your day to day activities in the days preceding the start of your period, and perhaps one of these changes is leading to the development of the boils. Try to keep track of whatever you do, and think about whether it could be related to the boils. Factors that can increase the risk of boils appearing include a lack of hygiene, general weakness or ill health, and nutritional deficiencies. These factors do not themselves cause boils to appear, but they may make it more possible for the bacteria to take hold and cause an infection. If you still cannot identify any cause, you should probably consult a doctor. This is especially important if you think you may have contracted some kind of sexually transmitted disease (STD). Your doctor will probably be able to tell from looking at the boils, and if necessary will recommend some tests.
answered by M W