The most common differences between symptoms of Bell's palsy and stroke are that stroke symptoms have a much more rapid onset and stroke usually preserves full motion in the eye and forehead, while Bell's palsy does not, the Journal of Emergency Medical Services states. Stroke is much more dangerous.
Bell's palsy is caused by damage to the major nerves leading to the face (there is one on each side), according to the Journal of Emergency Medical Services. Because just one major nerve branches out to control the muscles of each side, damage to that nerve effects that whole side. Stroke affects the brain, not the peripheral nerves. The signals for the lower part of the face come from just one side of the brain, while the signals for the eyes and forehead come from both sides. Because a stroke usually just affects one side, the eye and forehead will still receive signals from the other side, while the lower face is weakened.
The exception to this pattern is when the stroke is in the brain stem, in which case the whole side of the face can be affected, the Journal of Emergency Medical Services explains. In this case, other neurological symptoms can reveal which condition is causing facial weakness.