Researchers for the British Red Cross said their findings show the risks posed by heat are not matched by public concern.
Three in 10 people in Scotland also believe the country is not hot enough to suffer adverse effects from heatwaves, the charity added.
It comes as much of Scotland has baked in temperatures of 25C and higher for the past week, sparking water shortage and UV exposure warnings.
Nearly half (47%) of Scots have experienced negative effects from hot weather in the UK, including headaches, dizziness and heat rash, said the British Red Cross.
The charity expressed concern that high-risk groups such as the elderly do not see themselves as vulnerable from unusually hot weather, and its survey indicated 57% of people 75 and over did not feel unsafe.
In its report, Feeling the Heat, the charity called for more investment in adapting to a changing climate, including changes to buildings to manage heat levels and promoting green spaces.
Climate advisers have already warned that the UK Government is failing to ensure the UK can cope with the worsening risks of rising temperatures and extreme weather.
Urgent action is needed to deal with the threat of overheating in homes, power cuts and damage to nature, crops and food supplies from already inevitable global warming, the Government’s advisory Climate Change Committee said last month.
The Met Office last week issued its first amber extreme heat warning in England, similar to those issued when heavy rain or snow is forecast.
Met Office head of civil contingencies Will Lang said: “The UK is getting hotter. As a result of climate change, heatwaves are becoming longer and more extreme, and many people’s health and wellbeing will continue to suffer as a result.
“We already know that certain groups are more at risk from extreme heat, including people aged over 75, adults with underlying health conditions, children and babies, as well as people living in top floor flats and in built-up urban areas where temperatures are higher.
“With more hot conditions likely this summer, it is so important that the public understands the risks that heatwaves can bring, and to improve awareness of heat risk among the general public.”
Marie Hayes, Scotland director for independent living and crisis response at the British Red Cross, said: “Despite what many think, heatwaves in Scotland can impact us all.
“Every year people struggle with their health and wellbeing. Health and care services also see an increase in demand, transport is interrupted, and employers experience reduced productivity.
“But heatwaves don’t need to be deadly. From checking on your neighbours to providing first aid, simple early actions can keep you, your family and friends safe and well during hot weather.”
Opinium interviewed 2,000 UK adults online from June 11-15, 168 of whom lived in Scotland, with data weighted to be nationally representative of UK adults by age, gender, region and social grade.