Ask Tufts Experts

Why is it safe to leave cake out if it contains eggs? I thought foods containing eggs had to be refrigerated within 2 hours to prevent bacterial growth.

Raw eggs have a high level of water activity, making them an ideal breeding ground for bacteria like Salmonella. Egg-containing baked goods, on the other hand, do not provide a moist enough environment for bacteria to multiply, which is why your cake can safely sit out on the counter. Note that while cooking eggs reduces their water activity, eggs remain moist in foods like quiche and custard, so they do require refrigeration within 2 hours of cooking.

Is gum sold specifically for dry mouth more moistening than regular gum?

Chewing any gum stimulates the salivary glands and helps relieve chronic dry mouth, a condition known medically as xerostomia. But gum specifically for dry mouth may be better for protecting your teeth from decay, explains Nelson Rhodus, DMD, MPH, director of the Xerostomia Clinic at the University of Minnesota School of Dentistry. That’s because it contains zylitol, a sweetener that decay-causing bacteria cannot feed off of.

Last month you said the recommended amount of vitamin B12 is 2.4 milligrams. But my multivitamin lists B12 in micrograms. Which is right?

Your multivitamin label. Sorry for the 1,000-fold typo.