Small challenges can activate cells' protective systems. Scientists are exploring whether food compounds and medicines can make use of this effect. Our body's cells are constantly exposed to various hazards that could cause damage, malfunction, or even death. However, they have built-in defense systems that can sometimes be strengthened by small amounts of stress, a phenomenon known as hormesis. Researchers are investigating if food compounds and medicines can use these protective processes to improve health. Modern life often focuses on how environmental hazards affect major organs. For example, air pollution can damage the lungs and contribute to breathing disorders like asthma. While these effects are important, they often overlook the challenges faced by individual cells that make up every part of the body. Our cells regularly encounter various stresses, such as sunlight, alcohol, pollutants, and byproducts of some medicines. These stresses can damage DNA, the genetic material inside cells, as well as proteins and the fatty membranes surrounding them. If the damage is severe, it can cause cells to malfunction or die. However, despite these constant challenges, most of our cells adapt, survive, and function effectively throughout our lives. Cells have specialized stress responses that detect specific dangers and change the activity of genes that protect the cell. One well-studied example is NRF2, a protein that acts as a switch for hundreds of protective genes. When activated, these genes help cells reduce damage and remove harmful chemicals. Other stress responses help cells repair damaged proteins, fix DNA, or slow down cell division to conserve energy and prevent further damage. However, severe or prolonged stress can overwhelm these defenses and cause lasting harm. One of the most interesting features of these responses is their ability, under certain conditions, to turn a small challenge into a useful adaptation that makes cells more resilient. This dose-dependent pattern, where a limited exposure to a stressor stimulates a protective response while a stronger exposure causes harm, is known as hormesis. Exercise offers a familiar example: temporary strain on muscles, followed by recovery and repeated use, leads to adaptations that make them stronger and more capable of handling future demands. Some cellular stress responses may work in a similar way, helping cells better prepare for future challenges. Researchers have suggested that these responses may also help us deal with some of the chemical compounds produced by plants to protect themselves from pests. When we eat fruits and vegetables, some of these compounds may create a mild challenge that activates protective responses in our cells. Broccoli and other cruciferous vegetables provide an example. When they are chopped or chewed, they release sulforaphane, a compound that can activate NRF2 in laboratory-grown cells and animals. The evidence that eating broccoli or sulforaphane activates the NRF2 response in humans is still uncertain. A review of 18 human studies found mixed results, and many of the studies had methodological issues that might have influenced their findings. One challenge has been the inability to measure stress responses through simple blood samples. Researchers are now trying to identify biomarkers that would allow them to study the health benefits of sulforaphane and similar compounds more effectively. Fruits and vegetables provide fiber, vitamins, minerals, and many other compounds. Their health benefits come from complex interactions, with adaptive cellular stress responses potentially playing a role alongside these other mechanisms. Scientists have spent decades studying how cells sense and adapt to different stresses. Understanding how these protective responses are activated could be useful beyond nutrition. Researchers are now using this knowledge to develop medicines that activate cellular defense systems as treatments for various diseases. One example is omaveloxolone, which activates NRF2. In April 2025, it became the first medicine approved in the UK specifically for Friedreich’s ataxia, a rare inherited condition that progressively damages the nervous system and causes movement problems. In a 48-week clinical trial, people receiving the medicine performed better on a test of physical impairment than those receiving a placebo. However, as with all medicines, there are potential risks. Over-activating a cellular stress response could have harmful effects, so researchers must determine which stress responses can be targeted safely and which diseases could benefit. Hormesis does not mean that deliberately exposing oneself to pollution, ultraviolet radiation, or other hazards is beneficial. Nor does it suggest that supplements marketed as NRF2 activators are beneficial for healthy individuals. The dose, duration, and type of stress all affect how cells respond. Our cells are constantly exposed to potential sources of damage. When a challenge is limited, cell defense systems may adapt, leaving them better able to handle future stress. This process, hormesis, may help explain some of the health benefits of regular exercise and a diet rich in fruits and vegetables. As scientists learn more about hormesis and how cells defend themselves, carefully targeted medicines may offer new ways to treat specific diseases.