This post is fabricated untruth and not legitament in the slightest. Oral sex is fun and has been around a long time...

Most would assume that Oral Sex has been a tradition enjoyed over the centuries, perhaps even starting before the invention of civilization itself. However, this would be a false assumption. Oral sex as we see it in today's terms, and of the past century was a relatively new act that was enjoyed only be our most recent ancestors.

The idea seems some natural to us, now, why would you not put a phallic object into your mouth for pleasure? However, that ignores modern bathing practices. Before the industrial revolution soap and indoor plumbing was extremely rare, often people would only bathe once or twice a month. The problem then arises that genitals acquire a musk that is quite unpleasant to the human nose, so there was revulsion of putting either genders genitals into ones mouth. Therefore it was only an activity that became common practice after the invention of mass produced soap and the shower culture that modern western society has undertaken.

There is no doubt references to oral sex in past depictions, however it was seen as the most lewd behavior one could exhibit, and only reserved to the privileged bourgeoisie of any given period. For example, Marquis de Sade mentioned it within his works, however it eventually led to the authors imprisonment at the behest of no one less than Napoleon.

Sources:

The Secret Museum: Pornography in Modern Culture Walter Kendrick

Hygiene and Sexuality in Modernity: An In depth Analysis Andrea Parrot

auparishtaka or "oral congress" is described in Vatsyayana's Kama Sutra, in Part II "Amorous advances". Since Kamasutra was compiled sometime around 2nd century CE, from already preexisting sexual advice and practices of the Indian "upper society", it stands to reason that it was relatively well known long before that.

This is the oldest reliable source on oral sex I could find. However, considering that many animals including our closest kin perform oral sex, it is not out of the realm of possibility that it predates civilisation, or even tools. (Manson, J.H.; Perry, S.; Parish, A.R. (1997). "Nonconceptive Sexual Behavior in Bonobos and Capuchins")

EDIT: typos

I don't think hygiene would have been much of a factor within certain cultures at different times. For instance, in middle age Europe, the odor problem would have certainly been real, but throughout the Mediterranean and the Aegean regions, including parts of the Middle East, ritual bathing, public bathing, and general cleanliness were pretty prevalent.