If you are in the habit of using sunscreens regularly, it is time you watched out for some nano-particles, which, if accidentally eaten, could even result in death, recent research by scientists has revealed.

Research has revealed that particle size affects the toxicity of zinc oxide, a chemical used widely across all sunscreen brands. And particles that are smaller in size than 100 nano-meters could actually be more toxic to colon cells than conventional zinc oxide, says the study conducted by Philip Moos.

The researchers found solid zinc oxide to be more toxic than similar amounts of soluble zinc with the direct particle-to-cell contact being a pre-requisite to cause death of a cell. In fact, the study has raised concerns over the potential toxicity of nano-particles of chemicals that might have chemical and physical properties that are vastly different from larger particles of the same chemical.

Nano particles, which are less than 0.00005 percent the size of a human hair, are used in the food and cosmetics industry in a big way with sunscreens most often than not containing such particles of the chemical zinc oxide.

The study, published in the monthly journal ACS Chemical Research in Toxicology,  says that unintended exposure to nano-particles of zinc oxide is a public concern, especially in the case of children accidentally swallowing the sunscreen products.

The scientists conducted culture tests of colon cells and compared the effects of zinc oxide nano-particles to zinc oxide sold as a conventional powder to find that the nano-particles were twice as toxic as the larger molecules.

The study used isolated cells to analyze the biochemical effects of sunscreen lotions but did not consider the changes to particles during the passage through the digestive tract. It revealed that the concentration of toxic nano-particles to the colon cells was equivalent to consuming two grams of sunscreen lotion.