Your second sentence made me think of this.

It’s $3 per month for 200GB for me currently in the US.

This article is talking about benzene, not benzine FYI.

The allowable limit in drinking water by the EPA is 5 ppb. Inhalation exposure limit by OSHA is 1 a 5 ppm per day (inhalation is not an apples to apples comparison to consumption though). I’m not a toxicologist so I don’t know what exposure amount is “safe”, but dosage does matter.

This article mentions benzene coming from the carbomer in these formulas. The benzene is a residual impurity in the carbomer making process, and there are carbomer on the marketplace that don’t use benzene in their manufacturing process, but they are more expensive. I’m not sure the source of carbomer for these products, but I’ve seen reported on carbomer I’ve looked at to have up to 1 ppm of benzene impurity. Products like this might use carbomer up to 0.5 to 1%. So you’d expect maximum levels of benzene to be in the product (at the aforementioned levels) to be 10 ppb. So possibly at double the amount allowable in drinking water by EPA. People drink a lot more water than cough syrup (I hope) so it might not be that concerning.

The article frustratingly does not give amounts of benzene found in these products so it could be sensationalist—I just don’t know. So is benzene bad—yes. Does the cough syrup have concerning levels of benzene? Maybe, but just saying benzene might be present isn’t enough information in my opinion.

I think what you said is true but that also ketchup as a material is shear thinning—meaning as you shake or tap the bottle, this creates stress or “shear” on the liquid which causes the viscosity to decrease. It also takes a little bit of time for the liquid to re-thicken, so it will actually pour pretty well a few seconds after shaking it.

https://www.scientificamerican.com/article/ketchup-is-not-just-a-condiment-it-is-also-a-non-newtonian-fluid/

I haven’t heard that before but I don’t work on hair care products very often. Benzyl alcohol is used as a preservative in lots of cosmetic products though. It can be considered an allergen for some people, but overall it’s pretty safe (as far as we know so far).

It looks like the 91% natural ingredients version has benzyl alcohol as a preservative which is typically synthetically derived and in my experience can drastically shift the bio-based ratio.

As far as I can see, the rest of the ingredients are the same, but the sourcing of those ingredients could be different which could also shift the naturally derived percentage.

Can’t rule out that the furnace is dying—might be carbon monoxide poison you are experiencing.

Can see the before and after images in this article