The presence of a romantic partner during painful medical procedures could make women feel worse rather than better, researchers say.
A study involving 39 couples found this increase in pain was most pronounced in women who tended to avoid closeness in their relationships.
The authors say bringing a loved one along for support may not be the best strategy for every patient.
The work appears in the journal Social Cognitive and Affective Neuroscience.
Researchers from University College London, King's College London and the University of Hertfordshire say there has been very little scientific research into the effects of a partner's presence on someone's perception of pain, despite this being common medical advice.
They recruited 39 heterosexual couples and asked them a series of questions to measure how much they sought or avoided closeness and emotional intimacy in relationships.
Each female volunteer was then subjected to a series of painful laser pulses while her partner was in and then out of the room.
The women were asked to score their level of pain. They also had their brain activity measured using a medical test called an EEG.
The researchers found that certain women were more likely to score high levels of pain while their partner was in the room.
These were women who said they preferred to avoid closeness, trusted themselves more than their partners and felt uncomfortable in their relationships.
And researchers say the findings were mirrored in the brain activity tests too.
When their partners were present, the women's EEG traces showed higher spikes of activity in regions of the brain linked with experiencing body threat.
Dr Katernia Fotopoulou, one of the lead researchers, told the BBC: "Our research shows one piece of advice doesn't fit everyone.
"Advice that you must have your partner with you is not always going to work if people are most concerned about lowering the level of pain they feel."
Dr Amanda Williams, from University College London, provided an independent comment: "This research fits well with previous studies - some children report they feel more pain in the presence of their parents.
"This is particularly true when their parents are more anxious than them.
"People assume that having a partner, a parent or a close other present is always helpful but it is clearly not the case.
"We need to understand who this advice doesn't suit."