The "skateboard" helmets now on the market in big retail stores are almost all bicycle helmets in the classic old school skate style that Pro-Tec made popular decades ago. They have small vents, but their impact protection is designed for bike riding if the sticker inside only certifies that they meet the CPSC bike helmet standard. Most have better rear coverage than bike helmets do, and are more stable on the head because of that.

Most Pro-tec helmets look exactly the same on the outside, so you must find the standards sticker inside and be very careful about the model you buy for bicycling.