Silybum Marianum Seed Oil: Milk Thistle Oil vs Silymarin

Milk thistle is in the daisy family. People allergic to ragweed, chrysanthemum, marigold or daisies can react to it (NCCIH), so patch test the oil before using it on your face.

What is Silybum marianum seed oil?

Silybum marianum is milk thistle, a tall, purple-flowered thistle native to Europe. Its small, hard, dark seeds (botanically, fruits) carry two unrelated things in one package: a fatty oil, and a family of plant compounds known as silymarin.

When you see "Silybum Marianum Seed Oil" on a cosmetic label, or "milk thistle oil" on a bottle, it means the oil pressed or extracted from those seeds. Cold-pressed milk thistle oil is sold as a culinary oil in some markets; one study described it as popular on the Polish market and analyzed it alongside linseed, pumpkin and rapeseed oils (Rabiej-Kozioł et al., Molecules, 2023).

What is in milk thistle seed oil?

Milk thistle seed oil is dominated by two unsaturated fatty acids. In one analysis of Tunisian seeds, linoleic acid made up about 50.5% and oleic acid about 30.2% of the fatty acids (Mhamdi et al., Pakistan Journal of Pharmaceutical Sciences, 2016). Palmitic and stearic acids make up most of the rest (Najjar et al., Journal of Dairy Science, 2026).

The oil also carries vitamin E. A study comparing extraction methods measured alpha-tocopherol in milk thistle oil, with the highest level (0.62 mg per gram) in the enzyme-assisted extract (Liu and Zhang, Molecules, 2023). Cold-pressed oils in general keep more of these minor compounds than refined oils; our cold-pressed oils guide explains why.

Milk thistle seed oil vs silymarin: why they are not the same

Silymarin is the reason most people know milk thistle. It is a mixture of flavonolignans, mainly silybin (also called silibinin) and its relatives such as isosilybin and silydianin (Memorial Sloan Kettering Cancer Center). These compounds are fairly polar, which means they do not dissolve well in oil.

That has a practical result. Labs and manufacturers usually remove the oil first, then extract silymarin from the defatted seed with alcohol or other solvents (Azadpour et al., Current Drug Discovery Technologies, 2021). The seed cake left after oil pressing is itself studied as a source of silymarin (Bedrníček et al., Antioxidants, 2022). Researchers have even described getting silymarin into milk thistle oil as "a challenge" (Liu and Zhang, Molecules, 2023).

So a bottle of milk thistle oil should not be assumed to deliver the silymarin dose used in liver research. If a product claims meaningful silymarin content, it should say how much per serving.

Using milk thistle seed oil on skin

In skincare, the oil is used as an emollient, like other linoleic-rich plant oils. There is little published research on milk thistle oil specifically for skin conditions, so think of it as a moisturizing oil, not a treatment.

Tips for trying it:

• Patch test a drop on your inner arm and wait a day, especially if you have plant or pollen allergies.
• Store it in a cool, dark place with the cap tight. Oils high in linoleic acid oxidize more easily than oils high in saturated fat, and a sharp, stale smell means the oil has turned.
• Use a few drops on damp skin, alone or mixed into your usual moisturizer.

What silymarin research shows for the liver

Silymarin is the part of milk thistle that has been studied for liver health, and the results are mixed. In its summary of the research, the National Center for Complementary and Integrative Health (NCCIH) finds the human trials too inconsistent or too small to settle the question, whether the condition was alcohol-related liver disease, hepatitis B or C, or fatty liver disease. Two trials NCCIH paid for, one in hepatitis C and one in NASH, saw no advantage from silymarin. For type 2 diabetes, a handful of studies hint at better blood sugar control, which is still early evidence.

Most people take milk thistle by mouth without trouble, and when side effects do show up they tend to be digestive, like gas, an upset stomach or a bloated feeling (NCCIH). Memorial Sloan Kettering notes that milk thistle may interact with some medications, including sirolimus and warfarin. If you take any prescription medicine, talk with your healthcare provider before using a silymarin supplement. For more on choosing a supplement, see our milk thistle guide.

Find it at William's

We don't currently list milk thistle seed oil online; call the store to check what's on the shelf.

Here is what we do carry, depending on what you are after:

• Starwest organic milk thistle seed, sold by weight: whole seed for decoctions or for grinding fresh.
• Starwest organic milk thistle seed powder, sold by weight: ready to stir into food or smoothies.
• Now Silymarin Milk Thistle 300 mg, 100 veg capsules: a supplement for people specifically looking for silymarin.

If you are shopping for a seed oil with research behind it, our black seed oil guide covers another popular pressed seed oil.

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