Injury on cat's paw pads

Hi, my cat has had this 'injury' for about a week now. I've no idea what could have caused it and I don't know how to help it heal. She keeps licking her paw even though I'm trying to keep an eye on her. She isn't in pain when walking. She had something similar on the other paw, but it was inside the pad, whereas this time it's here. Any advice? (She's an indoor cat, unless I decide to take her out on a lead. My other cat is fine.)