HSTS headers are an essential security measure for protecting web applications from man-in-the-middle (MITM) attacks. By enabling HSTS, websites can ensure that users' data is encrypted and secure, even when accessing the site via HTTP. The HSTS header tells browsers to use HTTPS on subsequent visits, preventing potential attackers from intercepting data. With only 25% of mobile and 28% of desktop responses including HSTS headers, implementing this security measure in Node.js applications can significantly enhance web security. By setting the max-age parameter, enabling the includeSubDomains directive, and using the preload parameter, developers can effectively secure their web applications against MITM attacks.