Radon is a gas that you can't see or smell, but is present in nearly all the air around us. Everyone breathes in radon every day, usually at low levels. People who inhale high levels of radon are at increased risk for developing lung cancer. Radon is a problem in homes in which higher concentrations collect. Find out more about radon by taking this quiz.

BMI, or body mass index, uses weight and height to calculate weight status for adults. BMI for children and teens also takes into account gender and age because healthy body fatness differs between boys and girls and changes as they grow. This BMI calculator will help you determine if your child is at a healthy weight.

This assessment is valid for women between the ages of 21 and 69 who have had sexual intercourse at least once and who have not had a hysterectomy with removal of the cervix.

The vertebrae in your spine are cushioned by soft disks. When one of the disks in your neck—the cervical area of your spine—ruptures, the result can be neck pain. Watch this video to find out the possible causes and recommended treatment.

Plastic surgery is becoming more popular, with the most common procedure now breast augmentation, or enlargement. Contrary to what you may think, women with breast implants aren't immune to breast cancer.

Information on more than 370 topics, featuring illustrations designed to clarify complex anatomy and procedures.

Tap into this interactive encyclopedia for instant access to information on more than 835 diseases and conditions.

Enjoy good health at every age: know your body and how it works, eat well and stay active, and follow a plan for disease prevention.