Explanation

There are 10 clotting factors and they work as a relay, passing a baton which switches them on - from factor to factor in the same order each time. The last factor makes a very strong glue that can patch almost any hole in a blood vessel to make it stop bleeding. This process is called coagulation.

If you have haemophilia, either factor 8 or factor 9 is missing, so when the baton gets to where the missing factor should be, there's nothing there to pass it on. So, the glue never gets made, and you keep bleeding.

If you have all the factors, but your platelets won't form clots, you bleed too much. This is called Von Willebrand disease.