An emergency medicine consultant at Tallaght University Hospital in Dublin has said the emergency department has seen patients with serious sunburn presentations due to the heatwave.
Dr Jim Gray said these have included workers and sunbathers not wearing tops.
He said the department has also seen increased constipation attendances due to dehydration.
Dr Gray also said more patients were presenting with a syncopal episode (collapse) due to heat.
Patients with pre-existing serious conditions are more prone to health conditions, he said.
Dr Gray has advised people out in the sun to use SPF 50 every two hours and to wear a hat and sunglasses.
He said people should minimise alcohol consumption and take regular sips of water or other non-alcoholic drinks.
He also said people should avoid long periods in the sun and as food goes off faster in hot conditions, they should cook food well if using a barbecue.
The Irish Pharmacy Union has said chemists have seen an increase in the number of patients with hay fever, because of the high pollen count.
Many pharmacies are also reporting that more people are looking for treatment for sunburn and there has been an increase in demand for insect repellents and rehydration salts.
It said people are also seeking advice on storing medicines, as many need to be stored below a certain temperature.