Across the US, politicians, activists and transgender people are fighting over the right to access transgender medical care. Rarely is the care itself actually discussed. This is that discussion.

So far, most vaccines in the US are mRNA vaccines. These represent a new technology and are likely to take over the vaccine world. But how do they work? What are their weaknesses? Five experts explain.

Scientists explain what you need to know about the COVID-19 risks in the air, from how aerosols form to how to keep kids safe on a school bus.

How climate change and other human actions have combined to create conditions for explosive wildfires in California, Oregon and Washington state.