• Wear and tear theory - cells break down and become damaged over time.
• Genome instability theory -aging happens because the body loses its ability to repair DNA damage.
• Cross-linkage theory - aging is due to the buildup of cross-linked proteins, which damages cells and slows biological functions.
• Rate-of-living theory - an organism’s rate of metabolism determines its lifespan.
• Free radical theory - aging is due to the buildup of oxidative stress, caused by free radicals.
• Mitochondrial theory - mitochondrial damage releases free radicals and causes aging.

• Telomere theory - Telomeres protect the ends of your chromosomes as they multiply. Over time, telomeres shorten, which is associated with disease and aging.
• Programmed senescence theory - Cellular senescence occurs when cells stop dividing and growing, but don’t die.
• Stem cell theory - Stem cells can turn into other cells, which helps repair tissue and organs. But the function of stem cells declines over time, potentially contributing to aging.
• Longevity gene theory - This is the idea that certain genes extend lifespan.

It says that an organism begins aging after they have reached their peak of reproduction and have passed down adaptive traits.

• Mutation accumulation - This theory presumes that random mutations accumulate later in life.
• Antagonistic pleiotropy - According to this theory, genes that promote fertility early in life have negative effects later on.
• Disposable soma theory - The theory claims that when more metabolic resources are directed toward reproduction, the less is put toward DNA repair. The result is cell damage and aging.

• Advanced glycation end products (AGEs) - AGEs develop when fats or protein are exposed to sugar. High levels may lead to oxidative stress, which speeds up aging.
• Heat shock response - Heat shock proteins protect cells from stress, but their response decreases as we age.
• Damage accumulation - Normal chemical reactions damage DNA, proteins, and metabolites over time.

In most parts of the world, women live longer than men . This is due to several biological, social, and environmental factors.

• Estrogen is the female sex hormone, and has been found to have anti-inflammatory and immune-boosting effects, which may protect women from certain diseases.
• In contrast, the male sex hormone, testosterone may suppress the immune system.

• Eat a nutritious diet - Focus on fruits, vegetables, whole grains, and lean protein. Limit processed foods .
• Stay active - Aim for 30 minutes a day, 5 days a week.
• Avoid tobacco - Tobacco speeds up aging.
• Drink alcohol in moderation - Alcohol increases your risk of chronic disease.
• Attend regular checkups
• Know your family history - To have appropriate screening or get early treatment for potential chronic diseases.
• Engage your brain - by doing brain exercises.
• Wear sunscreen - Sunscreen protects your skin from UV radiation, which can cause premature aging.