Skin and soft tissue injuries are the most common injuries caused by being hit by airsoft bb's. They are also usually the most minor of injuries. Most skin impacts (contusions) will heal without any special care and without leaving any scarring. This is true for a typical injury from a gun chronographed at 400 fps with a 0.20 gm bb.
The injury result from physical disruption of the structure of the skin (cutaneous) and sometimes connective tissue under the skin (subcutaneous). There is disruption of blood vessels and chemical messengers are released from injured cells. Both of these actions result in some bleeding in the skin and increased flow of blood to the area of injury. This can be limited through indirectly applying ice and applying pressure. Do not directly apply the ice to the skin or apply it for longer than 15 minutes.
Skin Protection
The easiest way to protect against contusion is by providing a barrier between your skin and the incoming bb's. This is done with layering of clothing and/or use of thick skin coverings.
There are many specific products made for protecting various body parts, including but not limited to: