Ingrown hairs are usually caused by one of two things, either the hair follicle is infected because of bacteria that’s introduced during or after shaving or the new hair is growing back under the skin rather than breaking out as it grows.

As others have said, if you’re using a 5-blade replaceable razor head make sure you replace it monthly or more depending on how frequently you shave. A dull razor will remove and scrape more skin off of you in a jagged manner instead of just smoothly cutting the hair. Also don’t press too hard against your skin as you’re shaving, the razor should just glide on your skin with minimal pressure.

If you’re like me and have curly hair that frequently tries to grow back downwards, make extra sure that you aren’t shaving against the grain on your legs and butt. Pay close attention on your thighs and butt especially because the grain changes depending on whether you’re working on your quadriceps, inner/outer thighs, and hamstrings. You won’t get as close of a shave, but the hairs won’t be shaved below skin level and it will help prevent it growing directly into skin. The exfoliation I mentioned in a previous comment and keeping your skin softer and moisturized daily will also make a big difference.

To expand on what others have said, make sure you’re storing your razor in a clean area. Try not to keep it in the shower where it will be constantly getting wet and growing bacteria. You can try cleaning it with alcohol before using it if you need to. Also make sure that the body lotion you’re using is non-comedogenic, which is a fancy medical word for the fact that it’s designed to not get in your pores. If you choose to start epilating or waxing, over time your hairs will grow back a bit finer which will also help in the long run with irritation but you won’t see results like this for a few months.