About half of all cancer patients receive some type of radiation therapy, which uses ionizing radiation to kill cancer cells and shrink tumors. This therapy can be delivered from machines outside your body or from radioactive material inserted into your body.

Seasonal affective disorder (SAD) is a form of depression that affects people when they don’t get enough sunlight. Remember the John Denver lyrics: “Sunshine on my shoulders makes me happy ... Sunshine almost always makes me high.” Psychiatrists often recommend that, if you are depressed, you should spend a half-hour a day in the sun.

Sciatica is caused by damage to the sciatic nerve, which is the longest nerve in the body. This nerve controls the muscles of the back of the knee and lower leg and provides sensation to the back of the thigh, part of the lower leg and the sole of the foot.

If you have some memory lapses, go to the doctor with a positive attitude. The fact is that many different medical conditions may cause Alzheimer’s-like symptoms. You could be suffering from the effects of a high fever, dehydration, poor nutrition, reactions to medicines, thyroid problems or a minor head injury.

• The thymus, which is located behind the breastbone, is one of the organs of the immune system. The thymus is where immune cells – white blood cells – called T lymphocytes (T cells) mature. The thymus begins to shrink when we are young adults. By middle age, it is only about 15 percent of its maximum size.

One of the surest ways to reduce your exposure to UV rays is to stay out of the sun when it is the strongest. Those times in North America are between 10 a.m. and 4 p.m. in the late spring and early summer. Other ways to protect yourself are to wear protective clothing, such as a widebrimmed hat, long-sleeved shirt and long pants.

There are many types of molds, which are fungi that thrive where it is damp and warm. They reproduce by spreading spores, asexual reproductive bodies. Spores are invisible to our eyes, and they float through outdoor and indoor air. Molds that cause allergies include Alternaria, Aspergillus, Cladosporium and penicillium.

Salmonella bacteria are microscopic living creatures that spread from the feces of people or animals. Salmonella can be found in raw poultry, eggs, beef and unwashed produce. But, any food can become contaminated. Salmonella is the most common cause of foodborne illness in the United States.