An inquiry by a police watchdog into how a man held in West Mercia Police custody managed to smuggle a small blade into his cell found he had taped it to his groin.
The Independent Police Complaints Commission (IPCC) began an investigation after a man harmed himself while being held in Worcester.
The man, in his 40s, was discovered with a cut to his arm.
The IPCC said there had been no reasons for an "intrusive" search.
It added that the searches carried out by staff had been appropriate in the circumstances and within the law.
Commissioner Rebecca Marsh said the man had not made any complaints about his care, telling investigators he had been treated very well.
"This man had taped a small blade measuring about 4cm long by 1cm wide to his groin area, which only a full strip search would have detected.
"There were not justifiable reasons for officers to conduct the sort of intrusive search that would have found this."
The man had been arrested during the early hours of 23 June for failing to attend court.
He was placed in a custody suite, under supervision, until later that day when he was taken to a cell and given a meal.
The man then used the cell intercom to say he was bleeding and was found with a small cut to his arm.
He was taken to hospital but discharged himself.