Jessica is among the PEOPLE’s 25 Women Changing the World issue, alongside fellow stars Pink, Uzo Aduba, Gal Gadot and America Ferrera, as well as epidemiologist Dr. Celine Gounder, Whole Child International founder Karen Spencer and primatologist and anthropologist Jane Goodall.

Jessica is talking about her work as volunteer at the Humane Society of the United States and, obviously, her three-legged dog Chaplin.

The Humane Society of the United States volunteer, 40, supports the animal protection organization in its partnership with 200 U.S. school districts to bring plant-based menus into cafeterias and works with fashion brands to help them create cruelty-free products.

“The more success that I’ve been afforded in my industry, the more I’ve gotten to learn about what’s going on in the fashion world,” Chastain says. “I very strongly believe in buying products that are cruelty-free.”

Chastain, who has “adopted every animal I’ve ever had,” also favors a vegan lifestyle. “I don’t think everyone needs to be vegan,” says the Oscar nominee. “It just means helping create healthier choices for society and for our hearts at the end of the day.”

She does, however, want people to speak up on social media. “If there’s something that’s important to you, you can write about it and you can do so on your own platform,” she says. “You don’t have to be an actress or a journalist or run your own newspaper or have your own network to actually have a platform.”