Macmillan Cancer Support is worried about a lack of support for unofficial carers, some of whom take on the equivalent of a second job to look after loved ones.
The estimated number of unofficial carers in Scotland is almost 125,000, compared with 83,000 in 2011, the charity said.
The type of support ranges from giving medication and changing dressings to cooking and looking after finances.
Macmillan said family and friends spend an average of 17.5 hours a week looking after a loved one with cancer, while a quarter of unofficial carers spend more than 35 hours, the equivalent of a full-time job, looking after someone.
The charity’s Scotland director Elspeth Atkinson said: “We are going to see a continuing rise in the number of people caring for friends and family due to the increasing rate of people being diagnosed with cancer.
“It is therefore essential we have support in place for cancer carers so they can continue to look after loved ones without being overwhelmed or left to cope alone.
“Carers are often required to administer medicine so we need to make sure they’re supported in this if needed.”
The YouGov survey found that cancer carers from as young as 17 to people in their 80s are having to take on more responsibility for the person they care for. Almost 6,500 people across the UK took part.