The fungus produces medium-sized fruit bodies (mushrooms) with orangish caps up to 12 centimetres (4+1⁄2 inches) wide that develop green spots in old age or if injured.

Although the fungus is one of the most common in Central Europe, the species was not validly described until 1968 by German mycologist Frieder Gröger.

[5] The epithet of deterrimus is Latin, and was chosen by Gröger to highlight the poor gustatory properties of the mushroom, such as the bitter aftertaste and often heavy maggot infestations.

The cap skin is bare, greasy in moist weather and slightly shiny when dry.

[7][11] The dense, bow-like lamellae are pale-orange to pale-ochre and on the stipe basifixed or slightly decurrent.

In old age or in cases of injury they receive initially dark red, later grey green spots.

The fruit body smells harsh, fruit-like and first tastes mild, but then slightly resinous-bitter and nearly spicy or somewhat astringent.

The surface ornamentation extends to 0.5 μm high and is mainly from warts and short, wide ridges, which are linked through few fine lines to form an incomplete net (reticulum).

They are 4–6 μm wide and are sometimes protruded, but are often shorter than the basidioles (basidia in the early developmental stage).

They are slightly spindle-shaped and often have a tip resembling a string of pearls; their interior is hyaline or granular.

The cuticle of the cap is an ixocutis, whereby the hyphae are linked in a jellylike matrix, that can swell up in moisture to become heavily slimy.

The cap of L. deterrimus changes its colour in old age or if injured distinctly greenish and is common only under spruces, while L. deliciosus is native under pines.

The most similar and also the most closely related fungus is Lactarius fennoscandicus, a boreal to subalpine species.

[10] Lactarius deterrimus is mainly distributed in Europe, but the fungus has also found in areas of Asia (Turkey,[13] India,[14] Pakistan[15]).

[10] Lactarius deterrimus has traditionally been considered to have a strict mycorrhizal host specificity with Norway spruce.

Arbutoid mycorrhizal associations are variants of ectomycorrhiza found in certain plants in the Ericaceae characterised by hyphal coils in epidermal cells.

The mycorrhiza formed by L. deterrimus on both bearberry and Norway spruce show typical features such as a hyphal mantle and a Hartig net; the distinguishing characteristic between the mycorrhizal symbioses with the different hosts is that the hyphae penetrate the epidermal cells of bearberry, although there are also some differences in the form of the Hartig net, branching pattern, and colour.

Bearberry may function as a nurse plant to help re-establish Norway spruce in deforested areas.

[17][18] The fruit bodies appear from late June to November, but usually from August to October; overwintered specimens can be found in freezing days up to early February.

The most common insects found on the fungus are Mycetophilidae and Phoridae larvae, which populate even the youngest fruit bodies.

The following species have been isolated from the fruit bodies of L. deterrimus:[20] Abnormally developed milk caps infested by the parasitic sac fungus Hypomyces lateritius (syn.

They do not create gills; instead, the cap bottom is covered by an initially soft, white hyphen fungus, also known as a subiculum.

[3][12] Like L. deliciosus, this fungus is mainly stir-fried in butter or oil; if it is cooked in water, the flesh becomes very soft.

[25] As the fungus is often heavily infested by maggots, skilled mushroom pickers prefer young fruit bodies.

The urine discolours to red if a large amount of milk caps are eaten, but this is entirely harmless and is not evidence for an impairment to health.

Sesquiterpenes are widely distributed in nature and are found in plants as well as animals, for example in the juvenile hormone of insects.

[26] Young, uninjured fruit bodies of L. deterrimus have sesquiterpenoides in the form of fatty acid dihydroazulene-esters.