Police in St Annes are hunting for a man matching this description after a "sexual offence" at New Thursby Nursing Home.
Officers were called to the care home shortly before 5am on Sunday, August 4, after an unknown man in his 20s was found in a room with a resident.
Lancashire Constabulary are investigating a "sexual offence" that took place, but declined to give further details.
The suspect, described as wearing all black clothing, is believed to have broken into the nursing home by forcing his way through a ground floor window.
Police say a member of staff disturbed the man before he fled through the same window.
Officers are now hunting for a pale white man in his 20s, with a medium build and short dark hair.
Detective Inspector Jamie Lillystone of Blackpool Police, said: “This is a very concerning incident but I would like to reassure people that we are doing everything in our power to find the person responsible including working with a number of specialist units.
“We have a team of detectives working on the investigation and patrols have been stepped up the area. We do not want to concern people but would like to take this opportunity to remind people to make sure they secure windows and doors.
“The victim is being cared for by professionals and is being supported by specialist officers. Their family have been made aware.
“If you have any information at all that could help with our investigation – we need to hear from you. If you were in the area at around 5am and saw anything suspicious, or have any CCTV or dash cam footage that may be useful, please contact us. You can call us on 101 quoting log number 350 of 4th August.”