Blisters, not all runners get them, but those who do know that prevention is key. One of the best ways I’ve found to prevent blisters on my long runs and during ultra events is by taping my feet the night before the race/run.
If you can prevent problems, you should make every effort to do so when running ultras (good advice in general, but especially here). There are many types of tape you can use on feet. I use different tapes on different areas and various circumstances. Before I put any tape on, I use tincture of benzoin. This makes the tape adhere to my skin and not move around even if I cross a river or two.
Hepafix is a thin fuzzy tape without stretch that can be used on toes without the need to tape all other toes to prevent rubbing skin off. I have also used Hepafix to prevent chafing on my back from hydration packs or shorts.
Kensio tape, like Rock Tape or KT tape, is very flexible and stretchy and a little thicker than Hepafix. It is rough on the outside, so if you use it on toes you will need to tape all of them. I use Kensio tape on my forefoot for “shorter” long runs. It easily bends and stretches to the shape of my foot.
Elastiskin is a thick tape. It is not stretchy and restricts foot movement a bit. It is very rough on the outside. Tape all skin touching the outside of the elastiskin. I use elastiskin on longer races.
When taping your feet, you need to make sure that there are no spaces between pieces of tape or you will get blisters between the pieces. You also need to make sure that the tape is smooth on your skin so that you do not get blisters under the tape. Some people tape from toe to heel other’s tape across. Cover any exposed tincture of benzoin with a powder so that your sock doesn’t stick to it and create a blister. Some runners will put a lubricant over the tape and then put their sock.
Since we are talking feet here, I will also mention toenails and callouses. Short toenails cause less problems. I round mine out, so they are less likely to stab into the toe next to them. Other runners, square them off. I’ve never tried toe caps to prevent toes rubbing together, but they are out there as an option. Toe socks can help reduce problems, but keep in mind it makes your toes wider and may cause rubbing issues with your shoes and the outside most toes.
Callouses, some runners love their callouses and claim they prevent blisters. In my experience, the bigger the callous the more likely it is that I will get a blister under the callous. A blister under a callous is a major issue because it is difficult to drain the blister. A large callous makes your shoe fit differently as well, which is why you are more likely to get a blister underneath it. If you cannot bear the thought of parting with your callous, at least keep them to a minimum.