Thai Basil: Flavor, Botany and the Basils of Thai Cooking

The basil in a Thai green curry and the basil in phat kaphrao aren’t the same plant. The first is Thai basil, horapha in Thai: a form of sweet basil, Ocimum basilicum, with a stronger anise scent than the Italian kind and, often, purple stems. The second is holy basil, a different species with a different job. And in one Thai lab analysis, Thai basil’s oil was led by estragole, with geranial and neral behind it.

At a glance

What Thai basil is

Britannica lists Thai basil as O. basilicum variety thyrsiflora and notes that it’s common in Asian cooking.² PROSEA describes a var. thyrsiflorum with a densely branched flower head and loose whorls of flowers.⁴ Kew’s Plants of the World Online, though, treats the old name Ocimum thyrsiflorum as a synonym of Ocimum basilicum var. basilicum, which is ordinary sweet basil.¹ So botanically, Thai basil is a cultivated type of sweet basil, not a separate species. You’ll still see the variety name on seed packets and in research papers.

The native range of O. basilicum runs from tropical and subtropical Asia to northern Australia, with Thailand, Vietnam, India and Cambodia among its native regions. Where and when the Thai type was selected isn’t documented in any source we found. Claims that Thai basil came from Iran, or has been grown on the Indian subcontinent for 5,000 years, have no traceable source.

The basils of Thai cooking

A 2018 study from Chiang Mai University analyzed five basils “used as food ingredients in Thailand”: two holy basils, Thai basil, lemon basil and tree basil.³ These are the three you’re most likely to run into:

Holy basil (kaphrao)

Holy basil is a separate species, Ocimum tenuiflorum, native from tropical and subtropical Asia to the western Pacific. In Andy Ricker’s Pok Pok, it’s “holy or hot basil,” bai kaphrao in Thai, with a peppery flavor and a powerful aroma. Ricker notes that Indian grocers may sell it as tulsi and warns that “holy basil” labels sometimes end up on purple-stemmed Thai or sweet basil. Holy basil is considered sacred by followers of Hinduism. It’s the herb in the stir-fry phat kaphrao, where it goes in at the very end and gets stirred just until wilted.⁷ It can come across as clove-like too, though we found no source that measures that. See holy basil and Thai basil vs. holy basil.

Lemon basil (maenglak)

The names get tangled here. PROSEA gives maenglak as the Thai name of Ocimum americanum, which it calls hoary or American basil, and says the young leaves are eaten raw as a side vegetable in Indonesia, Malaysia and Thailand. Britannica calls lemon basil O. ×citriodorum,² and Kew treats that as a synonym of Ocimum × africanum, a hybrid of O. americanum and O. basilicum.⁵ PROSEA lists citral among the components of O. americanum,⁶ and the 2018 study found citral and neral alongside estragole in its lemon basil oil.³ PROSEA adds that the seeds swell into a gel in water and often go into sweet cooling drinks.⁶ See lemon basil.

Flavor and aroma

Thai basil smells of anise and licorice, more strongly than Italian basil, with a peppery, slightly minty bite. The 2018 Chiang Mai study backs up the anise. It found anise and citrus scents dominant in the oils of Thai basil, lemon basil and tree basil, and linked Thai basil to anise, lime-like and fresh aromas.³

The compounds

In that study, Thai basil oil distilled from fresh leaves of plants grown at the university’s research center was led by estragole (methyl chavicol) at 452.80 µg/mL, followed by geranial at 180.57 µg/mL and neral at 151.16 µg/mL.³ Those are concentrations in one set of samples, reported in µg/mL instead of as a share of the oil, so you can’t line them up directly against percentage figures for Italian basil. Estragole is also a main compound of sweet basil in general.⁴

You’ll often read that Thai basil’s oil is rich in eugenol and limonene. Neither shows up among the main compounds in the study above.

How Thai basil is used

• Thailand. Sweet basil is an important ingredient in Thai cooking, where it goes by horapha. Horapha goes into green and red curries, soups and stir-fries, and gets served raw with noodle dishes. It’s not a substitute for holy basil in phat kaphrao, which takes its name from that herb.
• Vietnam. In The Pho Cookbook, Andrea Nguyen lists Thai basil (húng quế) on her pho garnish plate with mint, culantro and rice paddy herb, and says she adds it in warmer months when it’s at its peak. She tells readers to add or subtract herbs as they like.⁸ So Thai basil is a welcome pho garnish, but nothing supports the idea that pho requires it, or that it matters more than any other herb.

Technique

Basil is one of the delicate herbs best added a minute or two before cooking ends, because long heat costs flavor and aroma. It’s often said that Thai basil holds up to long cooking better than Italian basil, but we found no source that tests it. If a dish ends up with too much, see too much basil.

Buying and storage

Look for bright, perky leaves on purple stems, ideally with the flower buds still closed. Thai basil is mostly sold fresh. We found no published shelf-life figure for it from a regulator or standards body. Storage tips for sweet basil apply: see how to store basil and can you freeze basil?.

Safety

Estragole, the leading compound in the Thai basil oil above, is the one safety question regulators have looked at for basil. The EU Scientific Committee on Food concluded in 2001 that estragole is genotoxic and carcinogenic, based mainly on oral studies in mice, and couldn’t set a safe exposure limit.⁹ In 2022 Germany’s BfR said the risk from estragole and related compounds in food can’t yet be conclusively assessed and made no consumption recommendation for consumers.¹⁰ Neither body singles out Thai basil, and neither tells people to stop eating basil. Our basil profile covers the estragole evidence in more detail.

The NIH’s National Center for Complementary and Integrative Health has no fact sheet on Thai basil or basil.¹¹ We couldn’t find a systematic review or health agency backing claims that Thai basil treats arthritis, prevents cancer or fights antibiotic-resistant bacteria, so we don’t make them.

Substitutes and comparisons

Ratio (Method): Italian sweet basil with a small pinch of fennel seed or a few tarragon leaves gets closer to Thai basil’s anise note than basil alone. Go easy on the add-ins. See Thai basil substitutes for the full list, and these comparisons:

• Basil vs. Thai basil
• Genovese basil vs. Thai basil
• Cinnamon basil vs. Thai basil
• Thai basil vs. holy basil
• Thai spices