In the United States, helmets designed specifically for bicycling differ from helmets made for skateboarding. Considerably fewer helmets are designed specifically for roller skating or in-line skating. The differences among helmet styles are based on the safety requirements of each sport, as well as applicable mandatory federal regulations and the manufacturers' adherence to voluntary standards.
According to the U.S. Consumer Product Safety Commission, in the United States bicycle helmets must comply with the CPSC safety standards. Helmets sold for other types of activities may comply with voluntary standards set by independent organizations. The Bicycle Helmet Safety Institute recommends looking for skateboarding helmets that meet the ASTM F1492 standard. Many skate-style helmets only meet the bicycling standard, and are thus inappropriate for skateboarding.
Bicycle helmets range from well-ventilated versions, typically used for racing and urban riding, protecting the top and upper part of the forehead and back of the head, to full head coverage models designed to provide extra safety for BMX and mountain biking. Skateboarding helmets provide full coverage to the back of the head and usually have less ventilation than bicycling helmets. Roller skating and in-line skating helmets are usually the same style as skateboarding helmets.
If you ride a bicycle and skateboard, you can buy a dual-certified helmet approved by ASTI for skateboarding and CPSC for bicycling, rather than buying two separate helmets.
Skateboard helmets are designed to take multiple blows before being replaced, but they aren't sturdy enough to withstand extreme force. Bicycle helmets are designed to take extreme force from one impact, as in a catastrophic collision with a motor vehicle, and should be replaced after one accident. If you roller skate or in-line skate, look for a helmet certified to CPSC standards for bicycling. Skating is similar to bicycling in that crashes are less frequent than in skateboarding, but injuries tend to be more severe.
Helmets marketed for skateboarding or skating, as long as they are not also advertised as bicycling helmets, do not have to adhere to any particular standard. To ensure quality, check that the helmet is labeled both on the box and inside the helmet as meeting ASTM F1492 and/or CPSC standards, as appropriate.