Aroma chemicals getting more allergenic over time

[PeeWee678]

Linalool can form hydroperoxides over time but what about other aroma chemicals with respect to allergenic properties?

My question is actually specifically about cinnamaldehyde: I have a bottle that's one year past its expiration date so I'm wondering if it could have become more allergenic in the meantime...

Maybe there's a list of often used aroma chemicals that will become increasingly more allergenic over time?

 

[pkiler]

Cinnamaldehyde is already allergenic when made.

 

[PeeWee678]

Cinnamaldehyde is already allergenic when made.

I'm very much aware of that; my question is specifically if it will get more allergenic over time. Thanks.

 

[Alex F.]

Allergenicity is among the many sensitive topics on here. It is a matter of importance in perfumery, of course, but there are no specialists on here and threads on the subject usually don't produce anything of value.
My guideline for aroma chemicals is that, unless I know otherwise, they have a limited shelf-life and deteriorate over time. So if I'm not sure whether something's still usable, I'd rather err on the side of caution and dispose of it.

However, here's what I found in Tisserand & Young, Essential Oil Safety, 2014, p. 73, on your specific question:
"In general, aged products are more likely to cause sensitization reactions. However, cinnamaldehyde may be markedly less allergenic in aged preparations, where it has oxidized to cinnamic acid, and in mixtures in which it can react with alcohols and/or amines to form non-allergenic compounds." (Note the "may", though.)

 

[PeeWee678]

Thanks Alex. Funny that Cinnamaldehyde is mentioned specifically in that piece of information.
Indeed, "may", so I guess it's simply time to buy me a new bottle.

 

[parker25mv]

Linalool can form hydroperoxides over time but what about other aroma chemicals with respect to allergenic properties?

My question is actually specifically about cinnamaldehyde:

The allergen problems of cinnamaldehyde do not stem from the same type of hydroperoxide formation that things like linalool, citronellol and limonene do.

I may be wrong about this, but in the case of cinnamaldehyde (and including cinnamic alcohols to a slightly lower degree), the problem stems from the ring being oxidized through biological processes after being absorbed into the body's cells. This then makes the molecule very reactive and able to bind to the amine groups of proteins (rather similar to the reactivity of quinone, which would be a long & complicated explanation; because the entire molecule is in resonance, the reactivity of the two oxygen atoms are connected despite being on opposite ends of the molecule).

This can be demonstrated by the fact that dihydro-cinammic alcohol and aldehyde have just as much allergen potential, despite lacking a carbon-carbon double bond where any hydroperoxide formation could occur.

I could attempt to give a more detailed explanation but it is probably much more complicated than you want to hear.

If you are looking to reduce the allergenic potential, things like alpha-methyl cinnamaldehyde are around 4.5 times less allergenic. (That methyl group has a tendency to reduce the reactivity rate of the aldehyde group)

You can also see my posts (especially my third post on page 2) in this discussion: Alright, I need help with this damn cinnamon note (thread started Jan 16, 2022)

 

[PeeWee678]

The allergen problems of cinnamaldehyde do not stem from the same type of hydroperoxide formation that things like linalool, citronellol and limonene do.

I know; it was just meant as an intro, an example.

Thanks for the information but I wasn't really interested in the mechanism of allergens. With regards to alpha-methyl cinnamic alcohol: not only is it not nearly as tenacious as cinnamaldehyde, I don't have it and can't buy it in Europe (importing is too expensive for the small amounts I buy).

I also don't really need it because cinnamaldehyde is potent enough in the blend I'm working on. I'm well below the IFRA limit. It's just that I was worried that certain allergens may become increasingly allergenic after they exceed their shelf life.

In short: I'm gonna buy a new bottle and ditch the expired one.

 

[parker25mv]

I have a bottle that's one year past its expiration date so I'm wondering if it could have become more allergenic in the meantime...

From what I understand, cinnamon oil will not get more allergenic over time.

Well, at least the cinnammaldehyde and cinnamic alcohols will not get worse over time, and that is the main problem.

Cinnamon leaf oil does contain just over 2% linalool, however, but that dwarfs in comparison to the allergen potential of the cinnamic alcohol.
(Also, cinnamon leaf oil does contain just under 3% eugenyl acetate, so it is possible that part could get worse over time as the eugenyl acetate slowly reacts with water over time and breaks apart, but that is another complex discussion)

I think cinnamon oil does contain around 8% limonene. (So that part maybe could be a small issue, but I think would still be nearly insignificant compared with the cinnamaldehyde) If you're worried about the limonene component at all, a trace amount of BHT or tocopherol could be added, to help resist oxidation.

 

[parker25mv]

It's just that I was worried that certain allergens may become increasingly allergenic after they exceed their shelf life.

Well yes, lots of things do. Limonene (found in high levels in all citrus oils), linalool (found in lavender), citronellol.
That's why sometimes a trace amount of BHT or tocopherol is added, and these should be kept away from exposure to light during storage.

We've discussed this all before many times in other threads.

 

[David Ruskin]

Cinnamyl alcohol ( a semi solid at room temperature), a potential allergen, will, over time, oxidise to cinnamic aldehyde. Cinnamic aldehyde ( a liquid a room temperature), a potential allergen, will, over time, oxidise to cinnamic acid. Cinnamic acid ( a solid at room temperature) is, as far as I am aware, not regarded ad a potential allergen. Thus, if anything, I would have thought that cinnamic aldehyde would become less of a potential allergen as there would be less of it present. This may be utter rubbish.

 

[PeeWee678]

This may be utter rubbish.

Or it may not be.

You see: Alex quoted something similar earlier in this thread so you're probably right David.
I wasn't aware of Cinnamyl alcohol oxidizing to Cinnamaldehyde so I did learn something new today

Thanks!

 

[David Ruskin]

All alcohols have, in theory, the potential to oxidise to their relevant aldehyde. Just as all aldehydes can, in theory, oxidise to acid.

 

[PeeWee678]

All alcohols have, in theory, the potential to oxidise to their relevant aldehyde. Just as all aldehydes can, in theory, oxidise to acid.

Damn, I've had 6 years of Chemistry (in school) but hey, that's over 40 years ago (and perfumery is just a hobby since a year or so).
Still.. really disappointed in my own feeble memory. So thanks for being gentle on me

 

[parker25mv]

Cinnamyl alcohol ( a semi solid at room temperature), a potential allergen, will, over time, oxidise to cinnamic aldehyde. Cinnamic aldehyde ( a liquid a room temperature), a potential allergen, will, over time, oxidise to cinnamic acid. Cinnamic acid ( a solid at room temperature) is, as far as I am aware, not regarded ad a potential allergen. Thus, if anything, I would have thought that cinnamic aldehyde would become less of a potential allergen as there would be less of it present. This may be utter rubbish.

Cinnamic aldehyde is roughly four times more allergenic than cinnamic alcohol.
(No doubt the reason cinnamic aldehyde is allergenic is because some of it gets oxidized to the aldehyde by normal biological processes in the body's cells, but usually things that have less fat solubility have a lower uptake into skin cells)
Since cinnamic alcohol is only around four times less allergenic, that is going to mean that any small traces of cinnamic aldehyde that form are going to be insignificant in terms of overall allergen potential. The oxidation of a small quantity of the material is not going to have much effect on its skin sensitising capability, we would expect.

I wasn't aware of Cinnamyl alcohol oxidizing to Cinnamaldehyde so I did learn something new today

Often cinnamaldehyde is considered a more desirable smell than cinnamyl alcohol.
However, traces of cinnamic acid really will change the smell, in a way that might not be desirable in many situations and could make things smell "off".
However, the situation is not entirely horrible because cinnamic acid is sometimes rarely used in low amounts as an ingredient in certain fragrances.