Michael Mancienne was booked for a foul on Gallagher after just 13 minutes with Preston captain Kevin Nicholls curling the resultant free-kick from 20 yards wide of the keeper's right-hand post.
QPR keeper Camp punched clear a Nicholls right-foot left-wing corner after 33 minutes.
Linesman Ian Nolan signalled to the referee he had spotted a handball by Martin Cranie after 34 minutes and referee Trevor Kettle pointed to the penalty spot.
Preston managed to miss the penalty for the third time this season, as Camp dived to his right-hand side to save.
After a poor first half, the second half got worse with the referee brandishing a total of seven yellow cards.
Rowan Vine, on loan from Birmingham City, was booked for dissent after 52 minutes, before Preston old boy Gareth Ainsworth was replaced by substitute Marc Nygaard after 56 minutes for the visitors.
Karl Hawley was put clear after an hour, but his right-foot chip went over the crossbar from 15 yards.
Martin Rowlands was booked for dissent and then Callum Davidson picked up his sixth yellow card of the season for a foul on Hogan Ephraim.
Preston made a double substitution with just over 20 minutes to play, replacing Gallagher and Hawley with Brett Ormerod and Simon Whaley.
Damion Stewart and Youl Mawene were both booked for fouls as the game became tetchy as both sides looked for a decisive goal.
Reserves top scorer with ten goals, Neil Mellor, was given just eight minutes at the end coming on as a substitute for Chris Sedgwick for the Lilywhites, but neither side could break the deadlock as time ticked away.