Testosterone Replacement Therapy (TRT) treats clinically low testosterone levels, a condition known as hypogonadism. The therapy involves administering exogenous testosterone to restore hormone levels to a healthy range. While TRT improves symptoms like fatigue, low libido, and muscle loss, it influences various body systems, including the integumentary system (skin, hair, and nails). Because the skin is a major target for sex hormones, introducing external testosterone can lead to noticeable changes in its appearance and function.
How Testosterone Influences Skin Physiology
The skin is highly responsive to testosterone because it contains numerous androgen receptors (AR) in cells like sebocytes and hair follicles. Testosterone, an androgen, binds to these receptors, altering the skin’s environment. These effects are amplified by the enzyme 5-alpha reductase (5α-R), which is abundant in the skin.
This enzyme converts testosterone into Dihydrotestosterone (DHT), a much more potent androgen. DHT acts locally within the skin, driving many of the noticeable changes associated with androgenic activity. The type 1 isoform of 5-alpha reductase is highly expressed in sebaceous glands and stimulates oil production.
Testosterone and DHT regulate the growth cycle of hair follicles and the activity of the sebaceous glands. The skin’s response is individualized, depending on genetic sensitivity and the concentration of androgens reaching the tissue.
Understanding Skin Redness and Flushing
Skin redness or flushing is directly related to TRT’s systemic effects on the blood. Testosterone stimulates erythropoietin (EPO) production in the kidneys, which signals the bone marrow to create more red blood cells (RBCs). This process can lead to erythrocytosis, or polycythemia, where the concentration of RBCs in the blood increases significantly.
An elevated RBC count causes the blood to become thicker and more viscous, which can slow its flow. This increased blood cell volume often manifests physically as a ruddy, flushed, or noticeably red complexion, particularly in the face and neck. This persistent redness indicates a systemic change in blood composition.
Generalized redness differs from temporary flushing caused by vasodilation. Localized redness can also occur at the administration site, especially with transdermal patches or injections, due to irritation or a mild allergic reaction. Systemic redness from polycythemia is the more significant concern, as persistently high RBC counts increase the risk of serious issues like blood clots, stroke, and high blood pressure.
Common Androgenic Skin Adjustments
Beyond vascular changes, the androgenic effects of TRT lead to adjustments in the skin’s glandular and follicular structures. The most frequently reported dermatological side effect is increased sebum production, resulting in oilier skin. This heightened oil production results from DHT binding to androgen receptors on the sebaceous glands, causing them to enlarge and secrete more oil.
Excess sebum is the primary factor driving acne development, often called “T-acne,” which affects the face, chest, shoulders, and back. When oil mixes with dead skin cells, it clogs hair follicles, allowing Cutibacterium acnes bacteria to proliferate and cause inflammatory breakouts. Acne severity is often dose-dependent and pronounced when testosterone levels rise rapidly, such as after an injection.
Testosterone also promotes terminal hair growth on the body, resulting in increased facial or body hair (hirsutism). Conversely, in genetically predisposed individuals, DHT activity can accelerate androgenic alopecia (male pattern baldness) by shortening the growth phase of scalp hair follicles. These hair changes depend heavily on a person’s genetic sensitivity to androgens.
Strategies for Managing Dermatological Side Effects
Managing TRT’s skin-related side effects requires both dermatological care and adjustments to the hormone regimen. For common issues like oily skin and acne, over-the-counter products containing salicylic acid or benzoyl peroxide help control oil and reduce bacterial growth. For more persistent or severe breakouts, a healthcare provider may prescribe topical retinoids or oral antibiotics.
Systemic changes, particularly polycythemia, require management by the prescribing physician, as self-treatment is inadequate. The first strategy involves adjusting the TRT protocol, such as lowering the dose or increasing the frequency of administration. This helps reduce peak testosterone levels, stabilize hormone concentrations, and mitigate the body’s overproduction of red blood cells.
If polycythemia persists, the primary medical intervention is therapeutic phlebotomy, which involves drawing blood to reduce the overall red blood cell mass and lower blood viscosity. This procedure is performed to maintain hematocrit levels within a safe range and reduce the associated cardiovascular risks. Consultation with a physician is necessary to determine the most appropriate course of action.