Analysis of more than 1.8 million searches by British internet users found that one in five health-related web queries were about pregnancy and childbirth.
Digital advertising company Exponential Interactive found that skin care and exercise or fitness are the next most common concerns, both accounting for 18.4% of health searches.
Weight loss, smoking, headaches, high blood pressure and diabetes also feature among the top 10 health issues for which Britons turn to the internet.
The data, which examined searches performed in May, also showed wide gender differences in online activity.
Men are 14 times more likely than women to be interested in vitamins, 10 times more likely to be interested in nutritional supplements and four times more likely in high blood pressure. Meanwhile, women are 12 times more likely than men to be interested in dental health and nine times more likely to be interested in vaccinations.
The investigation found that lawyers and retail managers are most likely to look at online health content compared with people in other fields.
"By looking at the way people actually behave online rather than what they may tell you can often challenge common-held assumptions.
"These insights offer providers of health services and products the opportunity to better tap into the unmet needs of potential customers."