A helmet configured to protect a human head against mild traumatic brain injury upon impact includes an outer shell and a liner consisting of pairs of fluid fillable flexible fluid chambers fluidly connected to each other by fluid connections between each of the pairs of fluid fillable flexible fluid chambers being spaced on opposite sides of the helmet and configured to fill a space between the head and the outer shell when the helmet is positioned on the head. Impact resistant flexible pads are also inside the liner and are spaced around an inner circumference of the outer shell adjacent to each of the fluid fillable flexible fluid chambers. A flexible inner shell inside the liner is configured to fit closely on the head. The flexible fluid chambers are configured to compress in response to impacting of the helmet on an impact side and to force liquid through the fluid connections to inflate fluid chambers on an opposite side of the helmet thereby cushioning the head against a rebound impact on the opposite side.