Scientists know why leaves turn yellow in the fall: Chlorophyll breaks down, revealing the yellow pigment that was there all along. But red? Red is a different story altogether. Leaves have to make a new pigment to turn red. Why would a dying leaf do that? Scientists don’t really know. NPR science correspondent <a href="https://www.npr.org/people/4494969/nell-greenfieldboyce"target="_blank" >Nell Greenfieldboyce</a> reports on the <a href="https://www.npr.org/people/4494969/nell-greenfieldboyce"target="_blank" >leading hypotheses</a> out there. Read more of <a href="https://www.npr.org/2025/11/05/nx-s1-5599152/why-do-leaves-turn-red-fall-foliage-autumn"target="_blank" >Nell's reporting on this topic</a>.  Interested in more seasonal science? Email us your ideas at <a href="mailto:shortwave@npr.org"target="_blank" >shortwave@npr.org</a>. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at <a href="http://plus.npr.org/shortwave"target="_blank" >plus.npr.org/shortwave</a>. Learn more about sponsor message choices: <a href="https://podcastchoices.com/adchoices">podcastchoices.com/adchoices</a> <a href="https://www.npr.org/about-npr/179878450/privacy-policy">NPR Privacy Policy</a>

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Fall foliage is still a mystery: Why do some leaves turn red?

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