Four parallel-group RCTs (n=1,013) were included.
Two studies described adequate methods of randomisation. One of these trials reported adequate allocation concealment and adequately described drop-outs, while the other reported no drop-outs. In three studies it was unclear if the treatment groups were comparable at baseline with respect to type of surgery or gender.
No pre-operative hair removal versus pre-operative hair removal (1 RCT with 3 treatment arms): there was no statistically significant difference in SSI between hair removal (by razor or cream the day before or the day of surgery) compared with no hair removal. The results for razor favoured no hair removal, while the results for cream favoured hair removal.
Hair removal on the morning of surgery versus the night before surgery (1 RCT with 4 treatment arms): the results for razor showed no difference between timing of removal, whereas the results for clipper almost reached statistical significance favouring removal on the morning of surgery.
Pre-operative hair removal by clipper versus removal by razor (2 RCTs): hair removal (night before or the morning of surgery combined) using clippers was associated with a significantly reduced risk of SSI compared with razor removal (RR 0.29, 95% CI: 0.10, 0.86; NNT 25).
Pre-operative hair removal by cream versus razor (2 RCTs): the findings were inconsistent. One study showed that hair removal using cream (the day before or the day of surgery) was associated with a non statistically significant reduction in SSI compared with hair removal using razor at the same time. The other study found no significant difference between hair removal using cream the day before surgery and razor removal the day of surgery.