It started off as an analysis of Xenomorph sweat, trying to figure out what it'd smell and taste like. I quickly realized that most scents originate from bacteria, which would be minimal to non-existant for Xenomorphs.
The next best thing would be urea. Urea is essential for the metabolism of mammals, and also a bonding agent (For say, p-cresol and o-cresol, two odor chemicals found in sweat. Though these likely aren't available to Xenomorphs), and it, and residues of the amino acids and chemicals used in its production are excreted through many different ways. Urine, sweat, etc.
This thesis assumes Xenomorphs are anything like vertebrae back on earth and have a digestive system at least remotely similar to theirs.
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One of the main components of sweat, urea, is not affected by chirality, it cannot have a mirrored/dextroversion:
The scent it is associated with is derived from residues of ammonia excreted along with it, which is a by-product of the production of urea.
Now, here's the deal, urea requires a ton of amino acids in order to be produced (levo amino acids, obviously), a short summary from Wikipedia:
Wikipedia wrote...
Urea is synthesized in the body of many organisms as part of the urea cycle, either from the oxidation of amino acids or from ammonia. In this cycle, amino groups donated by ammonia and L-aspartate are converted to urea, while L-ornithine, citrulline, L-argininosuccinate, and L-arginine act as intermediates
Hence, this could result in a significantly different smell and composure of both their sweat and other urea based excretions.
You see that "Arg" thing right below Urea in the urea cycle? Yeah, it stands for L-Arginine, you can get the dextroversion through a largely similar cycle. It's an extremely mild neurotoxic, pretty much a relaxing drug, a depressant, though excessive usage would actually result in additional stimulations, a stimulant.
A member of Colonial Marines, Troodon80, claims to have had personal experience with the substance as a depressant and states that it is, in fact, addictive.
Additionally, the dextroversion of "Asp" (stands for L-Aspartate), in order for it to be soluble like it's levo counterpart, it would likely bond with sodium, resulting in Sodium D-Aspartate, which is a natural performance enhancer [2], it massively increases the human body's production of testosterone, also resulting in an increased libido.
Finally, Orn, stands for L-ornithine. This amino acid allows for the disposal of excess nitrogen.
Dextroversion of this is largely similar in role, except for the fact that it is far more prone to create a hydrogen bond. (Including with molecules like ammonia, NH3)
Hence, it would demobilize the ammonia and eliminate the odor emanating from the production of urea to quite an extent.
So, so far, we can tell that Xenomorphs would not smell nearly as bad as those filthy humans, their sweat's a drug and a natural performance enhancer.
As for additional odors, that would be determined by MHC's and pheromones, which are too large and complex to even consider estimating with the limited knowledge we have at this time. Though the production of MHC's is also a key component of our immune system, so they might be considerably less common for Xenomorphs. (They might even have something completely different altogether).
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Remember, this is largely speculation, and I am by no means an expert, merely an enthusiastic amateur, so if you think there's anything you can change or debunk of my theory, be my guest. I'd be eager to learn.
But if you do agree, here's a question for ya: Licking a hunter or licking a larva?
