A bicycle safety expert said President Obama should have been wearing a helmet while he was bike riding on Thursday.

During a bike ride with his family in Martha's Vineyard, Obama did not wear a helmet while his two daughters did.

David Mozer, director of the Internional Bicycle Fund, said, "We encourage him to wear a helmet."

Mozer noted that Obama has worn helmets while bike riding before, adding that helmets "aren't as dorky as they were years ago."

White House spokesman Bill Burton said on Thursday he was unsure why Obama did not have a helmet on, saying, "I know he generally wears bicycle helmets."

Mozer pointed out the healthcare cost-benefits of buying and wearing a helmet, stating that head injuries are slow to heal and expensive to treat.

But Michael Bluejay of Bicyclesafe.com doesn't believe helmets are necessary.

In an e-mail, Bluejay wrote, "It's no more irresponsible to bike without a helmet than it is to drive without one. The benefits of helmets are largely unproven, especially considering that when helmet use surged in the 1990's, so did head injuries among cyclists. And the countries with the lowest helmet use also have the lowest fatality rate for cyclists. I promise you, if the head of any European country went biking without a helmet, it would be a non-issue, as it should be here."