All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
What comes out of pimples, whether it is blood or otherwise, is pardoned if it flows out on its own and not when someone intentionally causes it to flow. The Maaliki scholar Al-Hattaab said in Mawaahib Al-Jaleel: "This means that what affects the clothes and the body of blood or pus coming out of an abscess is pardoned if it comes out on its own but not if the abscess was squeezed." [End of quote]
The blood or any other fluid that you notice on your head is pardoned if you did not cause it to come out. Hence, the impurity will not transfer to your wet hair when you touch it. It is also pardoned in the prayer and does not invalidate Ghusl (ritual bath) or ablution.
As for the eyebrows, you must run your wet fingers through them in the Ghusl of Janaabah (bath to remove the state of ritual impurity resulting from sexual activity) and let the water reach the skin by wiping with your hands over them without exaggeration. Al-Hattaab also said in Mawaahib Al-Jaleel when speaking about Ghusl: "(And run his wet fingers through the hair), he referred to the hair in general so as to include all the hair that grows on the body. Ibn Al-Haajib said: 'The more famous view is that it is obligatory to run wet fingers through the beard, head, and other hair.' Ibn Farhoon said: 'He means by 'other hair' the hair of the eyebrows, eyelashes, mustache, and armpit and pubic area if there is hair on them.’" [End of quote]
Al-Hattaab also said about the hair of the eyebrows and other facial hair with regard to ablution: "If there is hair on the face, it is required to wipe it with one’s wet hand. If the hair is so heavy that it covers the skin such that it is not visible underneath it, then the obligation of letting the water reach the skin is waived and it is sufficient to wet the hair that covers it only. But, if the hair is light and the skin is visible through it, it is required to wipe over it along with the skin underneath it. This applies to all facial hair, whether it is on the cheeks, lips, or eyebrows." [End of quote]
Allah Knows best.