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Particles in sunscreen could be toxic if accidentally eaten

BMJ Group News

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Tiny particles in sunscreens could be toxic to cells in the gut if they are accidentally eaten, researchers have shown. They say that nano-particles of zinc oxide may be more likely to cause harm than conventional zinc oxide.

What do we know already?

Nano-particles, very tiny particles barely 1/50,000 the breadth of a human hair, are used in many products including cosmetics and sunscreens. But there has been concern about how safe they are, because they can act differently to larger particles of the same substance.

Zinc oxide is a common ingredient of sunscreens because it can block the sun’s rays. But traditional zinc-based creams tend to leave white residue on the skin, which some people find unsightly. Nano-particles of zinc oxide don’t leave a residue, so creams containing nano-particles have become a popular alternative.

The question is whether the tiny particles can cause any harm. Zinc is known to cause damage to the lungs if it’s inhaled as dust. Some doctors worry about what could happen if children accidentally eat sunscreens containing nano-particles of zinc.

New research has looked to see what happens to cells from the human gut if they come into contact with zinc oxide nano-particles. The research was carried out using cells grown in the laboratory, so it’s not a direct test of what might happen if the substance is eaten.

What does the new study say?

Zinc oxide nano-particles are more toxic (poisonous) than normal sized zinc oxide particles. The nano-particles of zinc oxide were toxic at concentrations about half that of normal sized zinc oxide. The researchers described the differences as “relatively modest”.

If particles of zinc oxide come into direct contact with the cells of the gut, they can cause the cells to die. This can cause irritation of the gut and vomiting. It’s not clear whether swallowing zinc has effects in the body outside the gut. In cases where people have eaten large amounts of zinc, they’ve suffered damage to their gut without harmful effects elsewhere.

You’d need to eat about 2 grams (under a tenth of an ounce) of sunscreen to get a similar concentration of zinc oxide particles to the one that caused gut cells to die in the laboratory tests.

How reliable are the findings?

While there’s no reason to doubt the reliability of the study findings, it is important to remember that what happens to cells in a laboratory is not always a good guide to what happens to people. The researchers say in the study that the toxic effect on the gut cells may not happen in people, because the zinc particles are likely to be dissolved in stomach acid, and so would not come into direct contact with cells in the gut. The study showed that dissolved particles did not cause the same reaction as solid particles.

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