Sexual Health STDs How Negative Feedback Loops Work in the Body By Elizabeth Boskey, PhD Elizabeth Boskey, PhD Facebook LinkedIn Twitter Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases. Learn about our editorial process Updated on April 21, 2021 Medically reviewed Verywell Health articles are reviewed by board-certified physicians and healthcare professionals. These medical reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more. by Matthew Wosnitzer, MD Medically reviewed by Matthew Wosnitzer, MD LinkedIn Twitter Matthew Wosnitzer, MD, is a board-certified urologic surgeon and physician scientist. He specializes in male infertility. Learn about our Medical Expert Board Print Negative feedback loops play an important role in regulating health in the human body. A negative feedback loop, also known as an inhibitory loop, is a type of self-regulating system. In a negative feedback loop, increased output from the system inhibits future production by the system. The body reduces the amount of certain proteins or hormones it creates when their levels get too high. Negative feedback systems work to maintain relatively constant levels of output. For example, the body maintains its temperature, calorie consumption, blood pressure, pulse, and respiratory rate based on negative feedback loops. David P. Hall / Getty Images Negative Feedback Loops Manage Production Imagine that the body is a factory making Product X, and imagine that making too much of Product X is expensive, wasteful, and harmful. This means that the body needs a way to slow down the factory when enough Product X has been made. It does this through a negative feedback loop. What that means is that the speed of production is sensitive to the amount of Product X. When it starts to build up, production slows. It might help to think of the factory as a great, big assembly line that stocks shelves at the end. When the shelves get full, the assembly line has to slow down since there's nowhere to put the product. Too much product building up can cause damage. However, if the shelves are empty, there's plenty of space on which to stock the product. The assembly line can speed up until the shelves are full again, with the goal of keeping the shelves filled at the right level all the time. The opposite of this would be a positive feedback loop. In that case, the more Product X there is, the faster the plant will make more. Examples Several well-understood negative feedback loops control a variety of different functions in the body. The female menstrual cycle operates through a negative feedback loop that involves structures in the brain, as well as reproductive organs, as follows. The hypothalamus is a gland in the brain that produces gonadotropin-releasing hormone (GnRH). The GnRH signals the pituitary gland in the brain to produce follicle-stimulating hormone (FSH). FSH triggers the ovaries to produce estrogen. High levels of estrogen (as well as progesterone and testosterone, which are regulated through similar loops) inhibit the production of GnRH. This causes the pituitary to make less FSH, which causes ovaries to make less estrogen. The male reproductive axis is set up in a similar manner as the female axis, with luteinizing hormone (LH), FSH, and testosterone in a negative feedback loop associated with fertility. How Hormones Take Charge of Your Menstrual Cycle Another negative feedback loop regulates vaginal acidity. The pH of the vagina varies depending on the specific bacteria that are present, as so: The normal vaginal pH is approximately 4—mildly acidic. This helps prevent the growth of problematic bacteria, including those that cause sexually transmitted infections (STIs). The lactic acid that maintains this pH is made by lactobacilli—part of the normal vaginal flora. These bacteria grow faster and produce more acid at higher pH. One of the hallmarks of bacterial vaginosis is a pH of above 5—which will trigger the normal flora to produce acid that prevents the infectious bacteria from thriving. When the pH gets close to 4, the lactobacilli can slow down the production of lactic acid. Seeking Homeostasis One key word that is important in understanding negative feedback loops is "homeostasis." Homeostasis is defined as a system's tendency toward stability. Homeostasis is very important in the human body. Many systems have to self-regulate in order for the body to stay in optimal ranges for health. Some systems that work through negative feedback to achieve homeostasis include:Blood pressureBody temperatureBlood sugarWhen individuals have problems maintaining these systems, a negative feedback loop will likely be poorly managed. For example, in diabetes, the pancreas does not respond properly to high blood sugar by producing more insulin. In type 1 diabetes (insulin-dependent diabetes, in which the pancreas produces little, if any, insulin), this is because there are fewer cells available to make insulin. A person's immune system has damaged the insulin-producing cells. Similarly, breathing regulates the body's oxygen and carbon dioxide levels—which are tightly controlled by the mechanisms in the brain that mediate respiration. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit 3 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Thiyagarajan DK, Basit H, Jeanmonod R. Physiology, Menstrual Cycle. [Updated 2019 Apr 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Amabebe E, Anumba DOC. The Vaginal Microenvironment: The Physiologic Role of Lactobacilli. Front Med (Lausanne). 2018;5:181. doi:10.3389/fmed.2018.00181 Garzilli I, Itzkovitz S. Design principles of the paradoxical feedback between pancreatic alpha and beta cells. Sci Rep. 2018;8(1):10694. doi:10.1038/s41598-018-29084-4 Additional Reading Boskey ER, Cone RA, Whaley KJ, Moench TR. Origins of vaginal acidity: high D/L lactate ratio is consistent with bacteria being the primary source. Hum Reprod. 2001 Sep;16(9):1809-13. Boskey ER, Telsch KM, Whaley KJ, Moench TR, Cone RA. Acid production by vaginal flora in vitro is consistent with the rate and extent of vaginal acidification. Infect Immun. 1999 Oct;67(10):5170-5. Kahn SE, Cooper ME, Del Prato S. Pathophysiology and treatment of type 2 diabetes: perspectives on the past, present, and future. Lancet. 2014 Mar 22;383(9922):1068-83. doi: 10.1016/S0140-6736(13)62154-6.