Scholars agree

My gums bleed while I'm fasting. Does that invalidate it?

No. Blood from between the teeth does not break the fast, as long as you do not swallow it deliberately. Spit it out and rinse. Nor is the fast broken by a bleeding wound, a nosebleed, or a routine blood test according to the majority.

The four schools concur on this.

The long answer

A fast is broken by what deliberately goes in, not by what comes out.

So:

  • Bleeding gums. Very common, especially when brushing. Spit the blood out, rinse, carry on fasting. If a trace goes down without your intending it, nothing is owed.
  • Wounds and nosebleeds. These do not invalidate the fast.
  • A blood test. Most contemporary scholars do not treat it as invalidating, the quantity being small.

Where it stops being unanimous is the withdrawal of blood in quantity — donation, or cupping. There is a real and old disagreement there, and anyone wanting certainty should ask a scholar of their own school rather than take a general answer.

The framework is the same one throughout: “It has been made permissible for you the night preceding fasting to go to your wives for sexual relations. They are a clothing for you and you are a clothing for them. Allah knows that you used to deceive yourselves, so He accepted your repentance and forgave you. So now, have relations with them and seek that which Allah has decreed for you i.e., offspring. And eat and drink until the white thread of dawn becomes distinct to you from the black thread of night. Then complete the fast until the night i.e., sunset. And do not have relations with them as long as you are staying for worship in the mosques. These are the limits set by Allah, so do not approach them. Thus does Allah make clear His verses i.e., ordinances to the people that they may become righteous.” (Qur’an 2:187)

And the practical rule that settles almost every first-Ramadan worry: if you did not intend it, and it was not food, drink or intimacy, your fast is fine.

What it rests on