Why Butternut Squash Hurts Your Hands

October 12th, 2011

Many a gardener will grow butternut squash, and eagerly watch the fruits develop, counting the days, hoping they’re not ruined by an early frost. Then harvest time, and the gardener can’t wait. They take the squash inside and immediately start cutting it up, about 5 minutes later they’re aghast and trying to figure out why their hands are red and peeling and constricted. Water doesn’t help, “What is going on?” they cry.

I was cutting up a butternut squash this morning and my hands got hurt again, just a little bit though, because I was careful to touch exposed flesh as little as possible. It got me wondering about the technical details of why it happened. I knew the broad strokes, as they were, but as a bit of a science geek I wanted to know more. Unfortunately after going on the Internet I found nothing but incorrect information, even Wikipedia had it wrong. You had one forum where some guys made a hearsay guess, and then people cite this as fact, and all over the Internet from forums, to blogs, to Yahoo answers, the incorrect information is repeated.

Suffice it to say, I decided someone needed to put the correct information on the Internet.

Before I tell you why your hands get wounded like they were dipped in acid when handling butternut squash, let me tell you what is NOT the cause.

That is not a residue, or glue, peeling off your skin. Many places attributed this to the sap drying over your skin like some sort of liquid latex, and then peeling off. Your skin is peeling, not a residue, that stuff cracking and falling off is skin. That is why underneath it gets pink, because it is new skin.

This is also not an allergic reaction or contact dermatitis, as so many people seem to think, because one guy found an article abstract that said that some people have an allergic reaction to butternut squash. This condition doesn’t happen to some people, it happens to everyone. It will even happen to different species, in fact a plant treated with the substance will react, and they’re not even in the same Kingdom as mammals.

Which is not to say that some people don’t get contact dermatitis from butternut squash, by all means, if you get a rash, or hives, or end up itchy, you might have that sort of a reaction. Peeling skin is not an allergic reaction.

What is actually happening is you’re getting a taste of the squash’s self defense mechanism. All squashes have this, including relatives like cucumbers and zucchini. In fact, most fruits have this to a greater or lesser degree, even things like apples.

Have you ever noticed how squashes will scab? If they’re wounded they will form a scab. This is one reason they can keep for so long. Have you ever noticed when harvesting a squash, or a zucchini, or a cucumber, the cut end will leak a liquid? That substance is what dries out the end of the stem, sealing it off.

Gardeners perhaps run into this problem more than most because we cook with fresh foods sometimes, right from the garden. Unfortunately in this case right from the garden isn’t best.

Many fruits (and remember, botanically, squash is a fruit) have this self defense mechanism where a sap is excreted when it is wounded to dry out the exposed flesh and seal it off to prevent further infection or damage. There are many animals or insects that have no qualms about eating under developed unripe fruit, the plants, however, want fruits to reach maturity so that it can, in the end, turn into the next generation. So this evolved as a defense mechanism. This astringent compound both results in an unpleasant flavor (unripeness) and it dries out the exposed flesh, creating a scab. So it both deters animals from taking a bite, and heals the bite should they give it a try. You’ll often see that on butternut squash, one bite mark, but no more, the animal learned. Of course animals have evolved too so some will have the gumption to still eat unripe fruits.

As the fruit ripens, this compound lessens. So this compound is less in fully ripe fruit. Some fruits, like butternut squash, are often picked early by gardeners, or the gardener does not realize that the fruit needs to ripen more after picking. This is often referred to as curing. A fully ripened and cured squash will not ooze sap when cut, only newly picked or unripe ones will. The one I cut up this morning was picked slightly under ripe (right before a frost scare that had me worried). I had let it sit for 2 weeks, and I would have let it sit for longer, a month at least, but I really wanted some risotto tonight.

So as you see, this drying agent is just the fruit’s way of self preservation. Without the ability to scab wounds, every scratch, dent, or bite mark would be an invitation to fungus and bacteria, just like on humans, so plants have evolved this ability to scab their wounds just like we have, and this substance that dries out and hardens plants, also dries out and hardens hands, resulting in a painful exfoliation process. To fix it you need to get the substance off your hands, so wash them thoroughly, and then you’ll need some heavy duty moisturizing lotion.

To avoid having this happen to you, make sure your squash are ripe and have had some time to cure and dry out a little bit before you use them, or wear gloves. If you grow your own squash you’ll know when they were harvested, but if you’re buying them this is more common in squash bought in the fall, than in the winter, for obvious reasons. Remember too that this is true for many fruits and vegetables, and you may notice it when peeling a fresh from the garden cucumber and the like, but winter squash are the king of the hill with this, and it is so much worse with them.

I am still interested in learning more about this substance, it is so strong I wonder if it has other uses. Being an astrigent, like calamine lotion, it could probably treat mosquito bites and poison ivy (which is an example of contact dermatitis).

53 Responses to “Why Butternut Squash Hurts Your Hands”

  1. John Gwinn  Says:

    This afternoon I peeled a butternut squash that had been stored inside for five months. I got a dark stain on my fingertips where I held the peeled squash prior to cubing. It was very difficult to remove but there was no peeling or cracking of skin. I’ve grown butternut for years but this was the first time anything like this happened.
    Most comments were helpful – especially the botany student and the administrator. I suspect the differences arose in just how much exposure the commenters had to the sap just under the skin (the thin yellowish layer)and whether it was cooked prior to peeling. It probably evolved, as others suggested, as a defense to damage to the skin. There would be no point for it to be in the flesh of the squash.

  2. Charmaine Alcock  Says:

    Thanks for sharing and providing me with a feasible explanation. I used half a butternut and stored the rest (unpeeled) with the cut side in contact with a saucer to exclude air and prolong shelf life. However, a few days later I had endless trouble trying to pry the butternut off the saucer – talk about superglue! Fortunately no adverse effects on my hands.

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