A survey of more than 500 carers for the Carers Trust found that 58 per cent said their mental health had been affected by being a carer.
More than a quarter (27%) of those questioned said the strain of looking after a loved one had affected both their physical and mental health.
Yet nearly two thirds (64%) of those polled said they had never accessed any support or services such as respite breaks or counselling. And six out ten (60%) of those that had been caring for someone for more than five years did so without accessing any additional support.
Anne Roberts, chief executive of the Carers Trust, said: "As this survey shows many unpaid carers have never accessed any support services to help them in their caring role.
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"We already know that many carers simply don’t have any awareness of the kind of help that is out there and what a huge difference it could make to their lives. We've launched Carers Trust so we can ensure that all carers know where to go to get that help when they need it and to help society recognise and value the role of carers in our communities across the UK."
According to the charity, there are now nearly six million unpaid carers in the UK, with more than 1.5 million aged over 60.
Nearly six out of ten (59%) carers also said their caring role had a negative impact on their working life.
Dame Judi Dench and Helen Mirren are among those supporting the charity.
Dame Judi said: "There are almost six million carers in the UK and the number is rising.
"Many of those carers are unaware of the support that is available to them and continue looking after their family or friends without any help and often at a cost to their own health and wellbeing."