What Causes side of foot blisters
These blisters are where the skin gets caught between the insole or footbed, and the upper of the shoe and can present as blood blisters.
Footwear- The width of your shoe is not wide enough on these areas and they pinch the skin causing a blister. If you measure around the 1st and 5th toe joints it is considered to be the widest part of your foot and the shoe manufactures base their shoe sizes on that area being the widest part of the shoe. So if you buy a wide fitting shoe, this where the width of the shoe would be at its widest.
Of the big and little toe, sadly these are inherited, so you can really blame the parents for this one!
If the edge of the foot hangs over the sandal then that exerts a pinching pressure and creates a blister, more often a blood blister. Moulded (shaped) sandal or shoe soles can have the same effect, where the edge of the sole cups the heel, if the heel of the foot is bigger than the sole, it will receive pressure from the edge of the sandal and the skin will blister. If the insole in the shoe has creased or moved, it can change the dynamics of the foot in the shoe. Maybe the shoe has had its day, we often see patients wearing well-worn shoes that are changing the way they walk as the shoes are so badly worn.
Either prescription or off the shelf ones can cause pressure if the orthotic is slightly too small , this could because the casting was taken early in the morning or when the foot was cold and some feet expand by the end of the day with temperature changes. This applies to buying the ones form the shop too.