A blackhead forms when the pores in the skin get clogged with dead skin and other debris. The tip of the blackhead turns black because exposure to the air oxidizes the debris, but the rest remains white underneath. Therefore when you gently squeeze a blackhead, you should express this material, including the black tip and the remaining whitish buildup.
It is generally best not to do this, because it is very easy to cause trauma to the pore and surrounding skin with too much pressure. When this occur, blood leaks into the pore and come out with pressure. In other words, the fact that you had significant bleeding
from the spot is evidence that you caused too much trauma with the squeezing. The risks of squeezing, therefore, including not only bleeding but also infection and permanent scarring.
Instead of this approach, the better way to take care of blackhead is by daily washing of the face, exfoliation, and the use of acne products containing benzoyl peroxide or salicylic acid. These products strip away the debris which clogs the pores and prevents the blackheads from forming.
If you have any further questions about the care of blackheads or your skin in general, you can talk to your primary care doctor
or your dermatologist