Regarding the question, we would like to quote Sheikh Yusuf Al-Qaradawi who stated:
I was asked about oral sex in America and Europe when I began to travel to these countries in the early 70s. We are not used to be asked these questions in our Muslim countries. Those Western people are accustomed to stripping naked during sexual intercourse. These are communities of nakedness, and from the licentiousness of the woman that she wears nothing to screen her body in her daily life.
So, they are in need of more excitements during copulation. However, men in our Muslim societies see nothing in the Muslim woman that can excite them on the basis of her wearing either Hijab (veil) or Niqab (face cover). But concerning whether being in complete nakedness during practicing copulation is lawful or not, the Prophet of Allah, peace and blessings be upon him, is reported to have said, “Guard your private parts except from your wife or your slaves.”
Muslim jurists are of the opinion that it is lawful for the husband to perform cunnilingus on his wife, or a wife to perform the similar act for her husband (fellatio) and there is no wrong in doing so. But if sucking leads to releasing semen, then it is Makruh (blameworthy), but there is no decisive evidence (to forbid it).
these parts are not dirty like anus, but it is ordinarily disgusting to man. But there is no decisive evidence to make it unlawful, especially if the wife agrees with it or achieves orgasm by practicing it. Allah, Exalted and Glorified be He, says: “And who guard their modesty, save from their wives or the slaves, that I heir right hands possess, for then they are not blameworthy, but Who so craveth beyond that, such are transgressors.” (Al-Mu’minun: 5-7)”
In the light of this, scholars maintain that the husband is allowed to enjoy his wife through any means of enjoyment except anal sex, for that is strictly forbidden.
Here, it should be noted that one of the main objectives of Shari`ah is to safeguard the life of people and keep them healthy. Based on this, if it is scientifically proven that oral sex or such practices cause mouth cancer or form any danger to the health of a person who practices it, then it becomes totally prohibited.