Social smokers are almost at the same risk of heart disease as daily smokers.
The Royal College of Physicians in Ireland says part time smokers have a 40 per cent greater risk of dying from smoking-related disease than non-smokers.
Women who smoke between 1 and 4 cigarettes a day are five times more likely to develop lung cancer.
The College has also raised concerns that occasional smokers are less likely to quit than those with a more regular habit.
One in five adult smokers in Ireland are occasional smokers but it's warning that most of them seem unaware of the risks.
Chair of the College's Policy Group on Tobacco Dr Des Cox says occasional and social smokers also need to be targeted in anti-smoking campaigns:
“Those who smoke occasionally have almost a 40% greater risk of dying from smoking related disease compared with non-smokers. They carry almost the same risk of cardiovascular disease as daily smokers.
In regard to lung cancers in women ages 35-49, those who smoke between 1 and 4 cigarettes a day are five times more likely to develop lung cancer when compared to non-smokers. In men, the risk is three fold.
“Until now, anti-smoking campaigns have targeted daily smokers and while they have been successful in reducing overall smoking prevalence in Ireland, the dangers of occasional and social smoking need to be included in these campaigns going forward."
Meawhile a fifth of under 25's are still taking up smoking with occasional smoking most common in this age group.
While data from the US also shows vaping is becoming more popular amongst teenagers.
Dr. Cox says," as a respiratory pediatrician I would have concerns regarding younger kids and young adults vaping because of developing lungs. If you're using the products there's a possibility you're causing excessive harm to your lungs."