The healing properties of propolis — a mixture of resin and wax made by honey bees to seal and sterilize their hives — have been known for many years. But its use in medicine and food supplements has been limited because the sticky substance is not water soluble and has a strong, off-putting smell. Now researchers have developed a way of purifying propolis that retains its medicinal properties, but makes it dissolve in water and eliminates its pungent smell.