It was first described scientifically by Jacob Christian Schäffer in 1774 as an Agaricus, and later transferred to the genus Lactarius in 1821 by Samuel Frederick Gray.

A mycorrhizal species, L. torminosus associates with various trees, most commonly birch, and its fruit bodies (mushrooms) grow on the ground singly or in groups in mixed forests.

Lactarius torminosus can be distinguished from similar species like L. pubescens or L. villosus by differences in morphology and coloration, or by microscopic characteristics like spore shape and size.

[11] A multi-gene molecular analysis published in 2008 demonstrated that species then distributed in the genera Lactarius and Russula actually consisted of four distinct lineages.

A proposal to conserve Lactarius with L. torminosus as the type was accepted by the Nomenclatural Committee for Fungi[13] and passed at the 2011 International Botanical Congress.

[8] The specific epithet torminosus means "tormenting" or "causing colic", in reference to the gastrointestinal distress associated with consuming the raw mushroom.

[15] Early English vernacular names were Gray's "bellyach milk-stool" (1821),[9] and James Edward Smith's "bearded pepper agaric" (1824).

[21] The cap is initially convex, but as it matures the center forms a depression and the outer edges rise until it assumes the shape of a shallow funnel; its final width is typically between 2 and 12 cm (3⁄4 and 4+3⁄4 in).

The latex that is produced when the mushroom tissue is cut or injured is white to cream, and does not change color with prolonged exposure to air, nor does it stain the gills.

As the cap enlarges, the margin, made of flaring filamentous hyphae that grow outward and downward, tends to curve inward, eventually forming a flap of tissue roughly parallel to the stem surface.

As further development takes place, these hyphae make contact with and adhere to the hymenial surface of the stem, covering basidia and macrocystidia (very long cystidia) already present.

Only the ornamentation on their surface is amyloid; it is partially reticulate (network-like) with interrupted ridges roughly 0.5–0.7 μm high, and a few isolated warts.

[22] Lactarius nordmanensis was described by Alexander Smith in 1960 to account for a North American species closely resembling L. torminosus in appearance, but with a slightly larger range of spore sizes (9–11 by 6.5–8 μm).

The closely related L. torminosulus is a dwarf version of L. torminosus, an arctic species associated with the birches Betula nana or B. glandulosa.

[29] Immature fruit bodies of L. scrobiculatus resemble L. torminosus, but they have a white latex that soon turns yellow upon exposure to air, and their stems have shiny depressed spots.

[35][36] Lactarius torminosus is a mycorrhizal species, and as such plays an important role in facilitating nutrient and water uptake by trees.

[39] Lactarius torminosus mushrooms may be parasitized by the mold Hypomyces lithuanicus, which produces a cream-ochre to cinnamon-colored granular or velvety growth of mycelium on the surfaces of the gills and causes them to be deformed.

[43] In a 1930 publication, Hans Steidle reported that although the mushroom was not toxic to "unicellular and cold-blooded organisms" when ingested, the liquid extract and the pressed juice of the fruit bodies, when injected under the skin of a frog, resulted in disturbed breathing, paralysis, and eventually death.

[44] Symptoms that are typically experienced after consuming raw mushrooms include nausea, vomiting, and severe diarrhea starting about one hour after ingestion.

[45] Despite the reports of toxicity, L. torminosus mushrooms are prepared in Finland, Russia, and other northern and eastern European countries by parboiling, soaking in brine for several days, or pickling, after which they are valued for their peppery taste.

[46] The nutrient composition of Finnish specimens has been analyzed and found to contain the following components (as a percentage of dry weight): protein, 17.20%; phosphorus, 0.46%; calcium, 0.12%; magnesium, 0.09%; potassium, 2.97%; sodium 0.01%.

[48] Fungal sesquiterpenes are commonly produced as toxins to defend against predation, and as a result some have chemical properties that may have applications in medicinal chemistry.