Unlike with motorcyclists, this is a surprisingly complex question. There are many people who, of course, say that bicyclists should strap on a helmet as a matter of course with every ride.
However, the data paints a more complex picture than this. According to bicycling.com, while overall the odds of a fatal head injury are lower when you wear a helmet, more must be done to actually protect cyclists when on American roads.
What are the arguments against helmets?
One of the major risks to cyclists is concussions. While wearing a helmet can add some protection in a crash, bike helmets do not do very much to protect against concussions. In fact, a 2013 study showed that cycling had the highest concussion rate of all sports studied, including American football.
So, yes, you should wear a helmet, but it will not protect you against everything.
What should we do to protect cyclists?
A 2016 study indicated that while helmet adoption is comparatively high in the United States, so is the risk of cyclist death per kilometer cycled. On the other hand, the Netherlands, where bike use is very widespread, reported low instances of helmet adoption as well as lower fatality rates.
The main difference between the Netherlands and the United States, many advocates claim, is that the Netherlands has far superior bike infrastructure. For instance, specific bike lanes are very common in Dutch urban areas, while they are not in the United States. It is also more common for bike lanes to have physical separation between the cyclists and the drivers of motorized vehicles.