Everyone offers health advice. But some “good” habits become harmful if taken to excess, says Erika Schwartz, MD, medical director of Cinergy Health, a Miami-based health insurer. The enduring pearls of wisdom below need qualifying before being taken as gospel.

Sanitize your hands to kill bacteria. Yes, cleanliness is important, but don’t be confused: Antibacterial gels and sprays aren’t a replacement for plain old soap and water. An under-the-faucet scrub is always the best and most efficient way to avoid illness, Schwartz says. “Regularly wash your hands.” Also, research from the Centers for Disease Control and Prevention (CDC) confirms that antibacterial soap is no better than regular soap and water in reducing bacterial counts and rates of infection.

Everyone should drink eight glasses of water each day. The idea that we all need to down 64 ounces of water a day, better known as the “8 x 8 rule,” is an oft-repeated chestnut. But some health experts disagree. No sound scientific evidence supports this recommendation, indicates an American Physiological Society report. The study concluded that the amount of water you need each day varies depending on your health. The important thing is that you know your own body and what it requires, Schwartz says. She also advises that you “drink the water over the course of the day and not all at once.”

Exercise is good for you. Physical activity is a fitness plus, but not over-exercising. If you forego the appropriate resting period, according to the CDC, you might experience bone and muscle injuries plus an increase in colds and flu as well as chronic aches and pains. “Give yourself a day to recoup,” Schwartz suggests. “Exercise should give you more strength and power—not drain you.”

Avoid dietary fats. Yes, but don’t cut all the fat from your diet. “A low-fat diet is good as long as it’s the bad fats [saturated fats from meats and trans fats from processed foods] you’re eliminating from your diet,” Schwartz says. “Fat is a crucial part of our body’s makeup. Without it you can’t make hormones and you can’t be in balance.” (Find good fats in foods such as olive oil, nuts and seeds, avocados and fish.) Also, low-fat diets won’t protect you from numerous diseases as previously believed, according to a study by the National Heart, Lung and Blood Institute.

Sit up straight! Parents insist we sit up straight to improve our posture. But Schwartz stresses the importance of using your abdominal (core) muscles to improve posture instead of forcing yourself erect by pushing up your shoulders. In addition, Scottish researchers found that sitting up straight can hurt your lower back. The scientists recommended that when seated you slightly lean back in the chair to avoid back pain.