When Justin Timberlake revealed that he’s been battling Lyme disease on Instagram, it lit up the internet. Some people sent well-wishes, others asked questions about the illness, and a few—of course—propagated bucket loads of misinformation.

As pop star Justin Timberlake shares his diagnosis of Lyme disease, his ordeal brings up questions. What is Lyme disease and its cause? How is the illness treated? A doctor explains.