Basil vs. Thai Basil: Same Species, Different Herb in the Pan

Here’s the surprise: Thai basil isn’t a separate species. It’s a cultivated form of sweet basil, Ocimum basilicum, the same plant as the Italian basil in your pesto.¹ Thai basil leans hard toward anise and has sturdier leaves, and you’ll usually wilt it into hot stir-fries and curries or eat it raw beside noodle soup. Italian basil is the softer, sweeter herb of tomato sauces and pesto. Each can stand in for the other, with a flavor shift you can see coming.

Side by side

The anise part has chemistry behind it. In a 2018 study of basils used as food in Thailand, Thai basil’s oil was linked to anise, lime-like and fresh aromas.⁵ For each herb in depth, see the basil and Thai basil profiles.

How to tell them apart

Sweet basil leaves are glossy and oval, with smooth or slightly toothed edges that usually cup a little, set opposite each other on square stems. Across the species, stems run from light green to dark purple and flowers can be whitish-purplish, white or creamy yellow, so color alone won’t tell you which basil you have. The giveaway PROSEA names for var. thyrsiflorum is the flower head: densely branched, with loose whorls of flowers.⁴

In Thai, horapha is the name for sweet basil, the species. People often take purple stems as the sign of Thai basil, but Andy Ricker warns that “holy basil” labels sometimes end up on purple-stemmed Thai or sweet basil, so stem color doesn’t guarantee anything either.⁸ Holy basil (kaphrao) is a different species again. See Thai basil vs. holy basil.

The difference in the oil

Both herbs share estragole (also called methyl chavicol) as a leading compound.⁴⁵ What changes is what sits next to it. The figures below come from different studies, measured different ways, so they show which compounds lead in each sample, not how much stronger one herb is.

The Thai study linked its Thai basil oil to anise, lime-like and fresh aromas, while PROSEA describes French-type basil oil as sweet-spicy, slightly green and fresh.⁴⁵ PROSEA recognizes at least six chemical types within O. basilicum, so any one basil plant could land closer to or farther from these samples.

Differences that change the dish

When it goes in. Basil is one of the delicate herbs best added a minute or two before cooking ends, because long heat costs them flavor and aroma. That suits Italian basil well. For Thai basil, Sherri Pengjad of Thai Foodie says it’s sturdier and holds up much better in hot dishes, and she stirs it into green curry right before serving.⁹ Either way, add it late. We found no source that tests how long either herb survives a simmer.

Raw on the plate. In Vietnamese cooking, Thai basil is one of the raw herbs served with pho. Andrea Nguyen lists it on her garnish plate with mint and other herbs, adds it when it’s in season, and tells readers to add or skip herbs as they like.¹⁰ So it’s a welcome pho garnish, not a required one.

In pesto and Italian cooking. The Italian uses of sweet basil are pizzas, pasta, chicken and cheese dishes, and pesto. Thai basil’s anise would change a pesto noticeably.

Can one stand in for the other?

Yes, with a flavor shift you can see coming. Both directions get more detail on Thai basil substitutes, and the amounts below match that page.

• Italian basil for Thai basil. Ratio (Attributed): Same amount. Nagi Maehashi of RecipeTin Eats calls normal basil the best substitute for Thai basil, though it lacks Thai basil’s slight aniseed flavor.¹¹ Pengjad also names Italian basil as the best substitute.⁹ Pailin Chongchitnant’s pad kra pao recipe lists holy basil or regular basil in the same 1 1/4 cups and notes that Thai basil will work too, which treats the basils as interchangeable by volume.¹² Add it at the very end and stir only until it wilts.
• To get closer to Thai basil. Pengjad suggests mixing Italian basil with a little mint, without giving amounts.⁹ Ratio (Method): Start with about four parts basil to one part mint, in the same total amount, and taste.
• Thai basil for Italian basil. In cooked tomato sauces it works if you don’t mind a licorice note. Ratio (Method): Start with a little less than the recipe’s basil and taste. In pesto, Caprese-style salads and other raw uses, the anise is front and center, so we wouldn’t swap.

Holy basil doesn’t stand in for either here. It’s a different species with a peppery, spice-like profile, and it’s the herb that gives phat kaphrao its name.⁵⁸

What isn’t known

• We found no study that compares Thai and Italian basil grown and analyzed the same way. The oil figures above come from separate studies with different units.
• No source documents where or when the Thai type of sweet basil was selected.
• The idea that Thai basil handles long cooking better than Italian basil comes from cooks; we found no test.

Safety

Estragole, a leading compound in both herbs, is the safety question regulators have looked at. In 2001 the EU Scientific Committee on Food concluded that estragole is genotoxic and carcinogenic, based mainly on studies in mice dosed orally, and couldn’t set a safe exposure limit.⁶ In 2022 Germany’s BfR said the risk from estragole and related compounds in food can’t yet be conclusively assessed. It named basil-containing pesto among foods that may contain high amounts and made no consumption recommendation for consumers.⁷ Neither body tells people to stop eating basil, and neither singles out Thai basil.

Related

• Basil and Thai basil profiles
• Thai basil substitutes
• Genovese basil vs. Thai basil and Genovese basil vs. sweet basil
• Thai basil vs. holy basil and holy basil vs. basil
• Cinnamon basil vs. Thai basil
• Cooking with basil, dried basil vs. fresh, how to store basil