No matter what style of riding you enjoy you will need to have a well fitting helmet to protect your head in the event of a crash. While any helmet is arguably better than no helmet at all, there is a good range of helmets that are specifically designed to suit certain styles of riding so if you spend more time on the road than careering down a mountainside you will want to choose a helmet which is specifically designed to meet your needs.
Road cycle helmets are designed to be lightweight and to withstand multiple impacts should you be involved in a collision with a car or other moving vehicle. It is important to note that wearing a helmet is no substitute for good road safety skills, so you need to be aware of other road users no matter how well protected you are. Other varieties of mens cycle helmets include those that are designed for specific sporting events such as triathlons or mountain bike racing and will have a different range of specs to allow for other types of impact so it's important to choose a helmet that reflects your particular style of riding.
The majority of adult bike helmets are fully adjustable to ensure a perfect fit and offer maximum protection in the event of a collision. A well fitting helmet will fit securely all around the head without being too tight and won't move more than an inch in any direction to ensure that your head is protected even after multiple impacts from the same crash.