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I have known 3 people in my life that have incredibly adverse reactions (one called it an "allergy" and his symptoms did resemble such) to consuming any form of green pepper (capsicum) but have no problems with red peppers (also capsicum). Besides the obvious chlorophyll -- which I rule out since none of these friends had issues with green vegetables -- what else is unique to the green peppers that could possibly cause such reactions?

My limited understanding is that green and red peppers (at least with bell peppers) are actually the same peppers at different stages of maturity. If that is true what changes within the plant during the maturation process?

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  • $\begingroup$ You mean chilli peppers, right? Peppers are actually a totally different species. $\endgroup$
    – WYSIWYG
    Commented Jul 5, 2016 at 8:06
  • $\begingroup$ Thanks for asking, I will clarify the question. Capsicum includes both chilis and bells, as did/do my friends' problems. $\endgroup$
    – O.M.Y.
    Commented Jul 5, 2016 at 21:26
  • $\begingroup$ @VanceLAlbaugh if you will note, in the question I wrote "red peppers (also capsicum)" $\endgroup$
    – O.M.Y.
    Commented Jul 5, 2016 at 21:44
  • $\begingroup$ Why all the down votes on this question? What is wrong with it? $\endgroup$
    – O.M.Y.
    Commented Jul 16, 2016 at 7:58
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    $\begingroup$ There cannot be -40; that would require 20 downvotes!! or reversal of 8 upvotes. Neither of which seems to be the case. You have given a bounty of 50 points. Those 50 points get deducted from your rep. You got 2 upvotes i.e. 10 points. So the net rep change on this question is -40. $\endgroup$
    – WYSIWYG
    Commented Jul 17, 2016 at 5:01

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Your limited understanding is indeed correct - the different colours indicate different stages of maturation, even though different colour cultivars exist (e.g. some that remain green even if fully ripe).

It is known that the different maturation states have different vitamin and/or mineral concentrations (see here or here). This indicates that different biochemical pathways are active and that therefore the enzymatic set-up is variable during pepper maturation (which could have an effect on tolerability as it might also affect other plant components).

Moreover, you are right that the green colour is - at least partially - caused by chlorophyll but also non-green bell peppers often have chlorophyll (Lancaster et al., 1997) but that probably is not the cause of your friend's responses.

More likely the cause is 3-isobutyl-2-methoxypyrazine (IBMP) which gives the characteristic (green) pepper smell and has highest concentrations in green peppers (that's why it is called green pepper smell). It has one of the most intense odours that can be detected at very low concentrations, even within the complex odours of wine (Pickering et al., 2007), according to Roth, 2014 perhaps even below PPT concentrations.

So how does this fit together? Pickering et al., 2007 also suggest that one should determine 'consumer rejection thresholds' for methoxypyrazines, indicating that it might be repellent to some people even in low concentrations of 1-2 ng per litre. This could explain your friend's aversion but evidence for the allergy component is dubious.

I did find one paper (Jensen-Jarolim et al., 1998) about allergen expression in peppers (birch allergy like). However, no green-specific allergens are reported, and it even seems like green peppers would be a better choice to avoid these allergens.

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  • $\begingroup$ Thank you. Very interesting about the odors. I am reluctant/cautious to use the term "allergy" myself, just passing on what one of my friends called it. His reaction to an accidental ingestion of a tiny amount (undisclosed odd ingredient in a potluck dish at a social event) was rapid onset of significant respiratory distress and intense nausea to the point of needing emergency medical intervention. I only observed one such incident but he advised there had been a few prior incidents over approx 50 years. $\endgroup$
    – O.M.Y.
    Commented Jul 13, 2016 at 14:59
  • $\begingroup$ @O.M.Y: That sounds quite weird, yes. But well, there are rare or unheard/unthought of allergies and now you know that there are green pepper-specific (or at least enriched) substances. So who knows ... Maybe your friend should have that checked. $\endgroup$
    – AlexDeLarge
    Commented Jul 15, 2016 at 12:12
  • $\begingroup$ It actually is 3 friends/aquaintances I've known through the years who have had this problem so it is not unique. All of them have consulted doctors, one has consulted an allergy specialist and had the whole "grid-of-pins-on-the-back" test. They tested positive on a whole range of usual's like shellfish and strawberries but also on odd items like vinegar, nutmeg, olives, and alcohol. Another friend (not one of the 3) has a weird allergy to real gold, makes their skin inflame soon after contact (but no reaction to other metals). Yes, they have been tested by a doctor also. $\endgroup$
    – O.M.Y.
    Commented Jul 16, 2016 at 5:49

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