As we age, our cells become less effective at talking to each other. This manifests in many ways, including a less capable immune system as well as disruptions in hormone levels and systemic blood factors.

Cells enter a state of senescence after dividing too many times or in response to things like DNA damage, oxidative stress, and mutations. Although senescent cells are no longer able to divide, they accumulate with age and secrete proinflammatory molecules that wreak havoc on their environment.

Alongside the accumulation of senescent cells and infectious pathogens over time, inflammation increases with age. This phenomenon is referred to as "inflammaging."

Across simple and complex animals, pathways that sense and respond to nutrients are consistent regulators of lifespan. The effectiveness of these pathways wane with age and this contributes to the likelihood of developing type 2 diabetes and other metabolic disorders.

Autophagy, which declines with age, refers to a cellular recycling program that removes old and damaged cellular components, such as mitochondria and proteins.

The gut microbiome, which plays important roles in metabolite production, nutrient absorption, and immunity, undergoes major shifts with age. Key changes include a loss of ecological diversity and a decrease in the number of beneficial microbes.

Epigenetic changes are modifiable and can influence gene expression. Over time, the epigenome becomes dysregulated and this results in genes being turned on that should be off and vice versa. DNA methylation, a type of epigenetic modification, tends to globally decrease with age.

Our cells are constantly making and repairing DNA. While the machinery that enables this is incredibly efficient, errors inevitably occur and mutations build up with age. Some of these mutations are harmful, such as those that give rise to cancer.

In our cells, proteins are the workers that accomplish necessary tasks. In order to work properly, however, new proteins must be correctly folded and old proteins must be efficiently disposed of. With age and in different neurological disorders like Alzheimer’s disease, proteins become misfolded and accumulate in harmful aggregates.

Mitochondria are the reactors in our cells that produce energy required for life. These cellular machines have their own DNA, produce free radicals, and can induce cell death in response to damage. Over time, mitochondrial efficiency decreases.

Stem cells have a unique ability to turn into many different kinds of cells. Because of this, they can replenish cells as they die off. However, the number of stem cells in our body declines with age and this leads to a reduction in regenerative capacity.

Telomeres are protective caps on the ends of our chromosomes that shorten every time a cell divides. When they get too short, cells become senescent and enter a zombie-like state.