DNA damage is not as dangerous as some people think. Our bodies have many effective mechanisms to repair cellular damage, and to protect the rest of our body from the effects of damage to any particular cell. Still, it is good to know about potential injuries that we can avoid. Here are some of the main things that damage DNA:
Ultraviolet light, found in sunshine as well as emitted by certain specialized light fixtures, can cause DNA damage. Ultraviolet light is light of wavelengths shorter than violet light but longer than x-rays. It is normally invisible to humans.
Ultraviolet light comes in threes types, A, B, and C. UVA harms DNA indirectly, by causing free radicals and reactive oxygen to form. UVB does direct harm. It adds energy to DNA molecules in the skin, which can cause adjacent cytosine molecules to bond with each other. When the DNA divides to replicate, the cytosine molecules are read incorrectly, and thus reproduced incorrectly. This causes a mutation, one commonly seen in one kind of skin cancer. UVC rarely harms humans because it is normally screened out by the atmosphere.
The way to avoid UVB damage is to wear modern effective sun block. It is also a good idea to avoid excessive sunshine, and to wear a hat, sunglasses, and, if appropriate, makeup. The vitamin D synthesized in sun-exposed skin is also found in fortified milk, oily fish, and multiple vitamins.
Ionizing radiation is radiation that creates ions. Ions are incomplete atoms, which may combine with other atoms in undesirable ways. Two kinds of ionizing radiation are x-rays and gamma radiation.
Background radiation comes from the sun, cosmic rays, the decay of minerals in the environment, and radon gas. However, the danger from this background radiation is very slight, because humans have evolved to tolerate it. The one exception might be the radon gas found in well-sealed houses in some areas. There is a simple home test for radon.
The biggest source of x-ray exposure is medical, and the largest medical source is in a CAT scan. Gamma rays are a component of cosmic radiation, and the occupational group most exposed to them is in-flight airline workers.
Copying errors can happen when DNA reproduces itself before cells divide. A tendency to such errors may be inherited, or may have to do with lifestyle. Errors also go up with age. Copying errors are a source of mutation. The mutation may produce defective cells that are prone to becoming cancer. Fortunately, humans have many effective mechanisms for dealing with copying errors and the defective DNA they can produce.
Cellular metabolism in itself is also thought to produce some DNA errors. Fighting infection, and repairing injury, the body may produce molecules that harm its own DNA. Taking good care of ourselves probably cuts down these kinds of errors.
Chemical exposure can seriously harm DNA. Certain hydrocarbons, such as benzopyrene, chemicals in cigarette smoke, in chemotherapy agents, and in air pollution are all harmful to some degree.
Cigarette smoke is to be avoided, obviously. So are solvents like TCE and TCA. Chemotherapy is a different kind of problem.
Some chemo fights cancer specifically by fighting DNA replication. Cancer cells are reproducing rapidly. Many cancer drugs attack the disease by interfering with cancer's DNA in order to slow or prevent this reproduction. At the same time, these particular drugs attack healthy cells, which have evolved to reproduce rapidly. That is why patients commonly lose their hair and/or feel nausea. Hair cells and intestinal cells are some of the most quickly reproducing body cells.
Cancer patients generally chose to endure the side effects, while making the best use possible of drugs that decrease side effects. Unfortunately, patients cured of one cancer may get another, years later, possibly from the effect of their treatment.
DNA is under attack on many fronts, but it has several mechanisms to defend itself. People can also give their DNA a hand, by avoiding behaviors that harm it, like baking in the sun, smoking, breathing radon, and ingesting toxic chemicals.