If there are two colors that define Halloween, they are black and orange. While black is an obvious reference to the more ominous symbols, i.e. evil creatures, the orange likely derives from the pumpkins carved into jack-o-lanterns.

Native to North America (northeastern Mexico and the southern United States), pumpkins are one of the oldest domesticated plants, having been used as early as 7,500 to 5,000 BC, the oldest evidence found in Mexico. Pumpkin fruits are a type of botanical berry known as a pepo.

The tradition of carving pumpkins into jack-o’-lanterns for Halloween originated in Britain and Ireland. People would carve lanterns from vegetables, particularly turnips, mangelwurzels, or swede. They continue to be popular choices today as carved lanterns in Scotland and Northern Irelands.

The practice of carving pumpkins for Halloween originated from an Irish myth about a man named “Stingy Jack”. The turnip has traditionally been used in Ireland and Scotland at Halloween, but immigrants to North America turned to the pumpkin which was more available and much larger. The name jack-o’-lantern did not appear until about 1837.

In the United States, the carved pumpkin was first associated with the harvest season in general, long before it became an emblem of Halloween.

The orange color in pumpkins comes from carotenoids which are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids can be produced from fats and other basic organic metabolic building blocks by all these organisms.

There are over 1,100 known carotenoids. They can be categorized into two classes, xanthophylls (which contain oxygen) and carotenes (which are purely hydrocarbons and contain no oxygen). All are derivatives of tetraterpenes, meaning that they are produced from 8 isoprene molecules and contain 40 carbon atoms. 

In general, carotenoids absorb wavelengths ranging from 400 to 550 nanometers (violet to green light). This gives pumpkins their deeply orange coloration. Carotenoids are also the dominant pigment in autumn leaf coloration of about 15-30% of tree species, but many plant colors, especially reds and purples, are due to polyphenols.

Carotenoids serve two key roles in plants and algae: they absorb light energy for use in photosynthesis, and they provide photoprotection via non-photochemical quenching. Carotenoids that contain unsubstituted beta-ionone rings (including β-carotene, α-carotene, β-cryptoxanthin, and γ-carotene) have vitamin A activity (meaning that they can be converted to retinol). In the eye, lutein, meso-zeaxanthin, and zeaxanthin are present as macular pigments whose importance in visual function, as of 2016, remains under clinical research.

And that’s where we’ll leave it.

Next time you see some orange Halloween decoration or a plastic jack-o-lantern, give a nod to carotenoids.