The free radicals of the human body are mainly oxygen free radicals. Excessive free radicals induce the body's oxidation reaction, which can damage the body's tissues and cells, leading to aging. So Harman proposed the famous freeradicals theory of aging.

Oxidative stress causes oxidative damage of biological molecules, causing the production of damage-associated molecular patterns (DAMPS) and the release of cytokines.

1. Free radicals and aging

Under normal circumstances, the generation and removal of free radicals in cells is in a dynamic equilibrium state. With age, this balance is gradually destroyed. As a result, the concentration of free radicals exceeds the "threshold", and chain free radical reactions make DNA, protein, especially polyunsaturated fatty acids and other macromolecular substances are denatured and cross-linked, which damages organelles, cell membranes and other structures, leading to oxidative stress damage to the organism, and eventually aging and death.

Therefore, Harman proposed the theory of free radical aging, which can be summarized as the intensification of the contradiction between the excess of ROS produced by mitochondria and the weakening of ROS defense capabilities, which ultimately leads to aging. In 1994, Barja et al. pointed out that the less ROS produced per unit of oxygen consumption, the longer the life span. The use of drugs or nutrients, calorie restriction (CR), and exercise are effective measures to delay aging. They can all increase antioxidant capacity and reduce the production of ROS, and become a powerful support for the theory of free radical aging.

2. Inflammation and aging

As we age, a chronic progressive increase in pro-inflammatory status appears in the body. Franceschi and others named this phenomenon inflammatory aging for the first time. The English term corresponding to inflammatory aging was first inflann-aging, and later literature appeared inflammaging, inflamm-age-ing and inflammageing. Xia Shijin and others first translated "inflamm-aging" into the Chinese term "inflammatory aging", and pioneered a series of studies on inflammatory aging mechanisms and interventions in China.

Inflammatory aging is closely related to a variety of senile diseases. The pro-inflammatory factors and anti-inflammatory factors in the elderly show ups and downs, and finally manifested as excessive pro-inflammatory response and imbalance of inflammatory homeostasis leading to inflammatory aging. Salviolii and other studies have shown that: pro-inflammatory cytokines play an important role in the body's inflammatory senescence caused by chronic inflammation.