Glossary.

Cross-linked, glucose-modified proteins formed when glucose non-enzymatically attaches to amino groups on long-lived proteins like collagen and elastin. AGEs stiffen tissue and reduce its ability to remodel. They accumulate over time and are not readily reversible, which is why glycation damage compounds.

The male-pattern hormones present at lower levels in women, produced by the ovaries and adrenal glands. Directly stimulate sebum production and follicular hyperkeratinization. Elevated free testosterone or DHEA-S drives adult hormonal acne, especially on the jawline and chin. Central to the PCOS pattern.

The stratum corneum's ability to hold water in and keep irritants out. Measured indirectly through transepidermal water loss (TEWL). Compromised by omega-3 deficiency, chronic inflammation, estrogen decline, and aggressive skincare. When barrier function drops, skin becomes dry, reactive, and prone to eczema.

The most abundant structural proteins in skin. Type I provides tensile strength; type III provides flexibility. Both have a slow turnover — dermal collagen has an approximate 15-year half-life — which is why glycation, photodamage, and hormonal decline compound over time rather than reset year-to-year.

The primary glucocorticoid hormone, produced by the adrenal glands in response to stress. Chronic elevation suppresses collagen synthesis in fibroblasts, raises blood glucose, promotes insulin resistance, drives inflammation, and disrupts sleep. Every other aging pathway worsens under chronic cortisol.

The sulfated form of DHEA, produced by the adrenal glands. The most abundant circulating androgen precursor in women. Elevated levels can drive sebum production and adult acne. Naturally declines with age.

The extracellular matrix protein that gives skin its ability to snap back after stretching. Produced only during a narrow developmental window; largely non-replaceable in adult skin. Damaged by chronic UV, glycation, and inflammation — which is why loss of elasticity is one of the earliest visible signs of skin aging.

The primary form of estrogen in premenopausal women, produced mainly by the ovaries. Directly supports collagen synthesis in dermal fibroblasts through estrogen receptor pathways. Decline at menopause drives approximately 30% dermal collagen loss in the first five years, with slower ongoing loss thereafter.

Nuclear receptors expressed throughout the skin — including fibroblasts, keratinocytes, and sebaceous glands. When activated by estradiol, they upregulate genes for collagen synthesis, hydration, and immune modulation. The mechanism through which estrogen protects skin structure.

A blood measurement of glucose concentration after an 8+ hour fast. Provides a daily snapshot of glycemic control, complementary to HbA1c's 90-day view. Elevated fasting glucose with normal HbA1c suggests recent change; both elevated suggests chronic pattern.

A blood measurement of insulin concentration after an 8+ hour fast. Often the earliest measurable signal of metabolic strain — shifting years before HbA1c or fasting glucose. Elevated fasting insulin drives IGF-1 signaling, sebum production, and androgen activity, and is a common feature of adult hormonal acne.

A protein that stores iron in cells. Serum ferritin reflects total body iron stores. Low ferritin — below approximately 40 ng/mL in women — is associated with pallor, dry skin, brittle nails, and hair thinning even when standard hemoglobin remains normal.

The cell type in the dermis responsible for producing collagen, elastin, and other extracellular matrix proteins. Fibroblast function declines with age, chronic inflammation, oxidative stress, and estrogen depletion. Also enters senescence — a state where the cell stops dividing but continues to secrete inflammatory signals.

The non-enzymatic attachment of sugar molecules to proteins, forming cross-linked, damaged structures called AGEs. The same chemistry that browns bread crust runs slowly through the skin dermis when circulating glucose is chronically elevated. Measurable through HbA1c and fasting glucose as clinical proxies.

A blood test measuring the percentage of hemoglobin that has been chemically bound to glucose over the previous three months. The strongest single proxy for cumulative glycation load and long-term glucose exposure of tissue proteins including collagen. Clinically normal below 5.7%; skin-longevity-optimized is meaningfully lower.

Menopausal hormone therapy — the therapeutic administration of estrogen (with or without progesterone) for menopausal symptom management. Peer-reviewed evidence supports dermal collagen preservation and skin thickness benefits in appropriately-selected women. Current authoritative framework: NAMS 2022 Position Statement.

A blood marker of chronic low-grade inflammation. Produced by the liver in response to inflammatory signals. The high-sensitivity version is calibrated to detect the small, sub-acute elevations that drive inflammaging and skin aging via MMP activity. The most clinically-available marker of the inflammaging load.

A hormone whose signaling is amplified by elevated insulin. Drives sebum production, androgen activity, and follicular hyperkeratinization — a central mechanism linking insulin resistance to adult hormonal acne. Also implicated in dairy-acne research (dairy raises IGF-1).

Chronic, low-grade, sub-clinical inflammation that accompanies biological aging and accelerates it. Coined in 2000 by Franceschi. Measured most practically through hs-CRP. Drives MMP-mediated collagen breakdown, compounds glycation damage, and worsens the hormonal aging trajectory.

A state in which cells become less responsive to insulin, requiring higher circulating insulin levels to maintain normal glucose. HOMA-IR is a calculated index using fasting glucose and insulin values. Common in PCOS, perimenopause, and chronic-stress patterns. Drives adult acne, skin tags, and metabolic-strain skin changes.

The predominant cell type of the epidermis. Produces keratin and forms the outer barrier layer of skin. Turnover slows from approximately 28 days in young skin to 60–90 days after age 60 — one reason interventions take longer to show visible effect in older skin.

Twelve consecutive months without a menstrual period, marking the end of ovarian estradiol production. Average age in the US is 51. Followed by measurable dermal collagen loss of approximately 30% in the first five years post-menopause, with slower ongoing loss thereafter.

A family of enzymes that cleave collagen, elastin, and other extracellular matrix proteins. Their activity is upregulated by chronic inflammation, UV exposure, and oxidative stress. Fisher's 2002 work established MMP activation as a central mechanism of both photoaging and chronological skin aging.

A blood test measuring the percentage of EPA and DHA (long-chain omega-3 fatty acids) in the membranes of red blood cells. The most reliable long-term marker of omega-3 status. Values below 5% correlate with impaired skin barrier function and increased inflammatory tone; 8% or higher is cardioprotective and skin-supportive.

An imbalance between reactive oxygen species (ROS) production and antioxidant defense capacity. Damages lipids, proteins, and DNA in skin — driving fibroblast senescence and accelerating chronological aging. Amplified by UV exposure, poor sleep, smoking, and chronic inflammation.

A hormonal pattern in women characterized by elevated androgens, insulin resistance, and cycle irregularity. Skin manifestations include jawline and chin acne, oily skin, skin tags, and androgen-driven hair changes (chin/upper lip hair growth, scalp thinning). Often amplifies through perimenopause.

The transitional years leading up to menopause, typically starting in the mid-40s and lasting 4–10 years. Characterized by erratic and progressively declining estradiol production, cycle irregularity, and the onset of the dermal collagen loss that accelerates through menopause. Where much of the visible my skin changed after 40 pattern originates.

Skin structural damage driven by chronic UV exposure. Includes accelerated collagen breakdown via MMP activation, elastin damage (solar elastosis), solar lentigines (age spots), and increased skin cancer risk. Accounts for the majority of what is commonly perceived as chronological skin aging.

The oil-producing glands attached to hair follicles throughout the skin. Their activity is regulated by androgens, insulin, and stress hormones. Elevated sebum production drives adult acne, oily skin, and enlarged pores. Sensitivity is often androgen-mediated on the jawline and chin.

The primary androgen. In women, produced by the ovaries, adrenal glands, and peripheral tissues. Directly stimulates sebum production and follicular hyperkeratinization. Elevated free testosterone drives adult hormonal acne, especially in PCOS.

A water-soluble vitamin required for DNA synthesis, red blood cell production, and cellular turnover — including the rapidly-dividing cells of the epidermis and epithelial linings. Deficiency shows up on skin as pallor with a yellow tinge, glossitis, angular cheilitis, and hyperpigmentation.

A fat-soluble hormone-vitamin that supports DNA repair after UV exposure, modulates skin immune function, and drives keratinocyte differentiation. Measured as serum 25-hydroxyvitamin D. Adequacy for skin biology typically means 40–60 ng/mL — meaningfully higher than the clinical cutoff for osteomalacia.

An essential trace mineral required as a cofactor in over 300 enzymes, including those involved in collagen synthesis, wound healing, keratinocyte migration, and skin immune function. Low zinc is associated with acne severity, slow wound healing, white nail spots, and increased skin infections.