Carers should be routinely screened for depression and mental health problems, doctors' leaders say.
The Royal College of General Practitioners (RCGP) warned that carers often "neglect" their own healthcare, and found that around 40% experience depression or psychological problems.
Holding routine appointments and maintaining a carers' register within GP practices could solve the "hidden" problem and prevent the £119 billion carers save the public purse being lost, the RCGP added.
Dr Clare Gerada, RCGP chairman, said: "Carers often neglect their own healthcare needs and in many cases it is only a matter of time before they themselves become ill.
"They are at risk physically and emotionally with stress-related illnesses but it can be hard for them to admit that they are struggling."
She told BBC Breakfast: "Unfortunately at the moment as with the rest of the health service, GPs are heaving under the workload and what this report is saying is that we have to target resources where they are most needed and they are most needed with carers.
"There are serious problems going on at the moment across the whole of the NHS but in particular in general practice, but what we mustn't do is forget the hidden group of those that need most care which carers are most certainly part of."
Dr Gerada said that the UK's seven million carers are a "critical asset" which need investment as "they already save the public purse £119 billion a year".
She said: "If carers fall ill you lose two patients. You lose the person they are caring for and also the carer so it makes financial sense to keep carers well."
The RCGP has drawn up a nine point checklist as part of new online guidance which also includes appointing a carers "champion" in all GP surgeries, and carrying out audits to measure improvements in carer support.