Excess sebaceous gland activity is caused by hormonal imbalances or by an enzyme named 5-alpha reductase, which converts testosterone into dihydrotestosterone (DHT). The quantity of these converting enzymes and receptors that capture the androgens (testosterone) present on the scalp varies from case to case and influences the amount of sebum that is produced. The seriousness of the seborrheic hair loss depends on how the enzymes and receptors are distributed on the scalp.

Both in men and women, the levels of 5-alpha reductase are much higher in follicles in the temporal, frontal and crown regions than in those of the parietal and occipital areas. The difference lies in the number of receptors in the follicles, which in women is much lower than in men, meaning that they are less subject to seborrhea and greasy hair. In women the defect may nevertheless occur and is generally related to hormonal or digestive disorders. For this reason, in the presence of hair loss accompanied by seborrhea, it is not easy to understand up to what point DHT is the common cause of both phenomena and at what point, in turn, the excess sebum becomes a relevant cause of the hair loss due to its specific ability to obstruct the hair follicles, thereby altering hair growth.

In practical terms, this translates into cases of androgenetic hair loss overlapping and coexisting with seborrheic hair loss. The components of sebum (cholesterol, triglycerides, free fatty acids, squalene and sphingosine) cause an acidification of pH and therefore a metabolic disturbance and cutaneous cell turnover. Moreover, altered levels of sphingosine, an amino alcohol that controls bacterial proliferation, worsen the situation leading to a condition of seborrheic dermatitis.

Another cause of this disease seems to be related to fungus of the Malassezia genus, in particular Malassezia furfur (previously known as Pityrosporum ovale) and Malassezia globosa, present in notable quantities in areas affected by seborrhea. However, no specific relationship with this fungus has been proven yet. An increase in cell multiplication can be observed in the affected areas. The production of sebum does not increase but changes its composition, thus irritating the scalp. Furthermore, the hair can become frizzy, messy, non-uniform and above all very oily. The condition can also involve the face (near the nose, mouth and eyebrows) and the auricle (outer ear). The basic treatment consists of trichological treatments aimed at removing excess sebum thanks to their hygienic and regenerating properties. Low frequency laser, with its hygienic and antibacterial properties, is also very useful for revitalizing the scalp, thereby supporting metabolic activity in hair follicles and bulbs.
Although accompanied by the risk of possible side effects, finasteride may be used as a pharmaceutical therapy.