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What is cancer? – Austin, 9, New York

Dear Austin,

I love a predictable schedule. Knowing when to eat, sleep and answer your questions keeps me chill.

That how the cells that make up our bodies work, too. They grow and die on a predictable schedule. Our bodies constantly make new cells to replace the ones that die. They grow for a set time and then die, too.

But sometimes cells grow out of control. They may grow faster or for a longer time than normal cells. They ignore the signals that tell a cell it’s time to die. They can even spread to other parts of the body and start growing there. That’s cancer.

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How does sunscreen work? – Seth, 6, Virginia

Dear Seth,

Since I’m a fluffy cat, my fur protects me from the sun. But my hairless cat and human friends use sunscreen when they go outside.

I asked my friend Michael Smerdon how it works. He’s a biochemist at Washington State University.

He told me that the sun puts out different kinds of light. Some light is visible to humans. Some is invisible—like UV light.

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