Many people who menstruate experience sudden chills, shivers, or shaking tremors around the time of their period, a recognized symptom often called “period flu.” The sensation of shaking is typically not a sign of infection but rather a physical manifestation of significant hormonal and metabolic shifts. Understanding these underlying physiological changes, from body temperature regulation to energy demands, is key to managing this monthly phenomenon.
The Link Between Hormones and Thermoregulation
The sensation of chills or shaking is closely tied to the dramatic fluctuation of reproductive hormones, specifically the sharp decline in progesterone and estrogen just before menstruation. Progesterone elevates the body’s basal temperature during the luteal phase. When this hormone level drops rapidly at the start of the period, it resets the body’s internal thermostat, triggering a temporary feeling of coldness.
This temperature change is often accompanied by prostaglandins, hormone-like compounds produced by the uterine lining to initiate contractions and shed the endometrium. When these prostaglandins enter the bloodstream, they can have systemic effects.
Prostaglandins act on the hypothalamus, the part of the brain that controls body temperature, raising the temperature set point. This causes symptoms similar to a low-grade fever. The body attempts to reach this new set point by initiating coldness and shivering, which is the involuntary attempt to generate heat through rapid muscle movement.
Metabolic Shifts and Circulatory Factors
Beyond hormonal influence, menstruation’s systemic demands can create metabolic imbalances leading to shaking. A common factor is hypoglycemia, or a dip in blood sugar, exacerbated by hormonal changes and altered appetite. Low estrogen can impact insulin sensitivity, and increased energy expenditure from cramping can cause blood glucose levels to fall.
The body responds to low blood sugar by releasing stress hormones like epinephrine (adrenaline), prompting the liver to release stored glucose. Epinephrine causes physical symptoms such as sweating, dizziness, a fast heartbeat, and shakiness. These symptoms warn that the body needs an immediate source of glucose.
Another contributor is the state of the circulatory system, particularly iron deficiency anemia. Heavy menstrual bleeding (menorrhagia) results in the loss of iron-rich red blood cells each month. If this iron is not adequately replaced, it can lead to anemia over time.
Anemia reduces the blood’s ability to carry sufficient oxygen, causing chronic fatigue and weakness. Low iron stores can also lead to heightened sensitivity to cold, contributing to chills and the shaking response.
Immediate Strategies for Relief
When shaking or chills begin, immediate actions can help stabilize the body and alleviate discomfort. Since hormonal fluctuations are difficult to manage in the moment, targeting metabolic and inflammatory symptoms is the most effective approach.
Taking an over-the-counter nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen, directly inhibits prostaglandin production. Reducing these inflammatory compounds can lessen cramping intensity, decrease pain, and minimize flu-like symptoms, including chills and shaking.
Addressing potential hypoglycemia involves consuming a small meal or snack containing both carbohydrates and protein. This combination stabilizes blood sugar more effectively than simple sugars alone, preventing a rapid spike and crash. Applying external heat, such as a heating pad or warm bath, can also soothe muscle contractions and counteract the feeling of coldness.
Recognizing When to Consult a Healthcare Provider
While period-related shaking is often benign, certain accompanying symptoms warrant a medical consultation to rule out underlying conditions. Consult a healthcare provider if the shaking is accompanied by a high fever, which may indicate an actual infection or a more serious condition.
Persistent or severe symptoms of anemia, such as extreme pallor, dizziness, or a racing heart rate, especially alongside unusually heavy bleeding, need professional evaluation. Heavy bleeding requiring changing a pad or tampon every hour for several consecutive hours suggests menorrhagia, which can lead to significant iron depletion. Any shaking that severely disrupts daily life or occurs outside the typical menstrual window should also be discussed with a doctor.