RESEARCH: Are Your Shoes Too Small?
Why do climbers opt for tighter shoes? A publication on shoe design for injury prevention in sport climbing attributed this to climbing shoes stretching significantly with continual use. At times as much as two sizes. To counteract, climbers surveyed usually bought shoes which were much too small in the hope that they would be broken in and stretch with use. In the age where the use of synthetic lining is becoming more common, this isn't always the case. They don't stretch much if at all.
Use of tighter shoes leads to bunions, calluses and foot pain. A UK study published in 2015 reported a 91% prevalence of foot pain in participants. This was higher than previous findings from past studies. The study suggests that ill-fitting and excessively tight footwear attributed to foot pain. To mitigate this pain, 77% of climbers surveyed in the study remove their shoes between climbs. However, they maintained the same choice in climbing shoe. 98% of participants used climbing shoes at least 1 UK size or equivalent smaller than their street shoe size. Most choosing climbing shoes 4 sizes smaller. In one instance, 6.5 sizes. Callouses, broken or brittle nails, foot numbness, cuts, bruises, pressure marks, and blisters were present in most participants.
There is a cultural acceptance of foot pain and ugly feet among climbers, and wearing overly tight shoes remains common practice. 'The tighter the better' became a kind of climbing mantra. With that, sore and calloused feet and eventual nasty bunions. The same 2015 UK study found an association of climbers of higher abilities seeking a tighter shoe fit. The preference for harder climbers to wear tighter shoes would, in turn, influence the beliefs and opinions of those new to climbing.
Longitudinal studies on climbers using exceptionally small shoes relative to street shoe size would be advantageous. But at present, there is a lack of shorter studies (referenced in this article).
If you are a conscious climber and value your feet and their longevity check out this article by Climbing.com which summaries climbing shoes and how to find the perfect fit. Because "... even a foot condom needs to fit your foot well—tight but not painful, no dead air space or pressure points, and good forefoot mobility. "