Menstrual cycle The first period usually begins between twelve and fifteen years of age, a point in time known as menarche. They may occasionally start as early as eight, and this onset may still be normal. The average age of the first period is generally later in the developing world and earlier in developed world. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women and 21 to 35 days in adults (an average of 28 days). Menstruation stops occurring after menopause which usually occurs
Immune cycle Immune cycle The immune cycle is a natural homeostatic oscillation of the immune system when chronic inflammation is occurring. Similar to the menstrual cycle, the exact wavelength and waveform of each particular individual patient is different. That is, different people have different immune cycles although each cycle is typically repeated every seven days. C-reactive protein levels in the blood need to be measured every few days in order to have enough time points to show a repeating fluctuation (a wave-like cycle). This is caused by the synchronous division of T cells over time, with T-effector cells boosting immune activity followed