A cheap and easy way to deep condition your locks? The answer is mayonnaise! I've tried it myself a few times, and it made my hair a lot smoother and shinier. The egg in mayonnaise has protein which helps strengthen hair (good for people who are on a mission to grow their hair out, like me). Apply mayonnaise to dry hair. If your hair is on the oily side, apply from the hair shaft down to the ends. Leave it in for 20 mins. If your hair is dry, you can leave it in longer if you like.