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Creative Touch Permanent Makeup and Aesthetics

Sex hormone binding globulin

Protein Protein

Sex hormone binding globulin (SHBG) is not simply a transport protein. It is the principal regulator of androgen and bioavailability, binding and DHT so tightly that the bound fraction is rendered biologically inert. The clinically significant figure is free testosterone, not total. SHBG levels are themselves highly responsive to metabolic state: , elevated androgens, and reduced oestrogen all suppress SHBG, whilst thyroid activity and oestrogen raise it. During perimenopause, falling oestrogen suppresses SHBG, paradoxically increasing free androgen availability even when total testosterone remains unchanged.

Sex hormone binding globulin (SHBG) is a liver-produced homodimeric glycoprotein that circulates in blood as the primary binding protein for androgens and oestrogens. It binds testosterone, (DHT), and 17β-oestradiol with high affinity. Crucially, what it binds cannot act on tissue receptors. In a typical adult woman, only around 2% of circulating testosterone is free; the remainder is bound to SHBG (approximately 20–44%) or loosely to albumin (approximately 78%). Free testosterone, not the total figure, is what androgen-sensitive tissues – including , , and dermal – actually respond to. [4]

Binding Hierarchy and What It Means

SHBG does not bind all sex hormones equally. DHT has the highest binding affinity (Ka ≈ 2.69 × 10⁹ M⁻¹s⁻¹), testosterone the second highest (Ka ≈ 1–2 × 10⁹ M⁻¹s⁻¹), and 17β-oestradiol somewhat lower still. This hierarchy has a practical consequence: when SHBG levels fall, DHT bioavailability increases disproportionately, because DHT was the most tightly sequestered in the first place. For androgen-sensitive tissues like the hair follicle’s cells, where DHT drives the androgen receptor signalling that shortens in (AGA), SHBG is not a passive carrier but an active buffer against excess androgenic stimulation. [4]

The free hormone hypothesis – validated in vivo by Laurent et al. (2016) in transgenic mice expressing human SHBG – confirms that the SHBG-bound hormone fraction is biologically inert. Androgen bioactivity was suppressed in androgen-sensitive tissues despite markedly elevated total testosterone in SHBG-overexpressing animals, confirming that it is the free fraction, not total concentration, that determines tissue response. [3] A clinical corollary: two clients with identical total testosterone readings can have meaningfully different androgenic tissue exposure if their SHBG levels differ. Total testosterone without SHBG context tells an incomplete story.

What Regulates SHBG

SHBG is not a fixed background variable. It responds to metabolic and hormonal state in ways that directly affect sex hormone bioavailability, and the regulatory inputs are precisely the factors that shift during midlife and perimenopause.

Oestrogen raises SHBG. This is the primary reason women generally have higher SHBG than men of similar age. As oestrogen falls during perimenopause, SHBG levels decline alongside it. Lower SHBG means more free testosterone and DHT available to tissue receptors, even when total androgen levels have not risen. [1]

and metabolic status suppress SHBG. The liver is an insulin-responsive organ, and elevated insulin directly reduces SHBG secretion. Research from the Study of Women’s Health Across the Nation (SWAN) confirmed independent associations between increased liver fat, reduced SHBG, and increased metabolic risk in peri- and post-menopausal women. [2] This creates a compounding pattern at midlife: declining oestrogen lowers SHBG, and if insulin sensitivity also declines, SHBG falls further, amplifying free androgen availability through two independent routes simultaneously.

raises SHBG through hepatic signalling pathways, partly via reduction of liver fat. (common in perimenopausal women) can therefore contribute to altered SHBG independently of sex hormone levels. [2]

Androgens themselves suppress SHBG creating a feedback dynamic where elevated free androgens further reduce SHBG, releasing more free androgens. In conditions of androgen excess (such as polycystic ovary syndrome), this loop can sustain and amplify the androgen environment. [4]

The Perimenopause Paradox

The SHBG dynamic during perimenopause produces an effect that is counterintuitive but well-evidenced. Total testosterone either stays roughly stable or declines modestly during menopause. Yet free testosterone – the biologically active fraction – can effectively increase, because SHBG is falling faster than total androgen is. Post-menopausal women with low SHBG and sustained androgen production can therefore experience a relative hyperandrogenic shift: increased facial hair growth, hair thinning, production changes, and flares, despite not having elevated testosterone on a standard blood panel. [1]

This is not a minor edge case. It is a common clinical picture at perimenopause that is frequently missed when only total testosterone is tested. The relevant clinical measurement is calculated free testosterone – derived from total testosterone, SHBG, and albumin concentrations – and the Vermeulen calculator is the currently preferred method for this estimation when direct equilibrium dialysis is not available. [4]

Genetic Variation in SHBG

SHBG levels are substantially heritable (estimates range from 30–80%) meaning significant inter-individual variation in SHBG exists independently of metabolic state. Several well-characterised SNPs in the SHBG gene (including rs12150660 and rs6258 at the SHBG locus on chromosome 17) are associated with measurably different SHBG concentrations and binding affinities. The rs6258 variant reduces SHBG’s binding affinity for testosterone, resulting in 22% higher free testosterone in CT vs CC genotype carriers despite similar total testosterone levels. [4] This is why two clients with similar lifestyle, age, and hormonal profiles can respond very differently to androgenic stimulation. Some of the variation is written into their biology before any environmental factor operates.

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Clinical Application

The clinical question that SHBG creates for an aesthetics clinic is a precise one: when a client presents with androgen-driven changes – scalp hair thinning, increased facial hair, oily , adult-onset acne – are those changes driven by elevated androgen production, or by reduced SHBG making the same total androgen level more biologically available? The answer determines what is addressable and what realistic expectations look like.

That question matters because the treatments we offer work on tissue-level responses to androgens. They cannot modify circulating SHBG. What they can do is address the consequences of elevated free androgen availability at the follicle and skin level, and do so more effectively when the clinical picture is understood clearly.

Phase 1: Understand What You’re Working With

For clients presenting with perimenopausal or post-menopausal androgen-pattern changes alongside normal or low total testosterone, the clinical framing should be explicit: this is likely a SHBG-driven relative androgen excess, not a primary androgen elevation. The practical implication is that lifestyle factors affecting SHBG – insulin sensitivity, metabolic health, thyroid function – are meaningfully relevant to outcome. A client actively working to improve insulin sensitivity is also improving their SHBG status, and by extension modifying the androgenic environment that is driving their hair or skin presentation. That connection is worth making explicitly during consultation.

Weight loss (particularly ) adds a further SHBG consideration. medications (semaglutide, ) that produce rapid weight loss trigger axis activation and elevation, which compounds the insulin-sensitive suppression of SHBG. For clients on these medications presenting with hair shedding, the clinical picture is likely multi-factorial: GAS6 suppression via cortisol elevation (as established in the and entities) operating alongside the SHBG-mediated androgen shift.

Phase 2: Address the Follicle and Scalp Environment

(iPRF) is the primary treatment for androgen-influenced in this client group. The mechanism is not direct androgen suppression (iPRF does not modify SHBG or DHT levels) but it addresses what androgen-driven follicle decline has produced: reduced dermal papilla cell (DPC) IGF-1 secretion, impaired anagen signalling, and attenuated perifollicular vasculature. iPRF delivers , , , and directly to the follicle environment, restoring the trophic signals that androgens have progressively withdrawn. It is not counteracting the SHBG-driven androgen excess; it is working with what the follicle can still respond to, restoring growth capacity in follicles that have not yet miniaturised completely.

(CAP) contributes through a genuinely distinct route. Its Wnt/β-catenin activation in DPCs directly stimulates anagen initiation, independently of the growth factor receptor pathways that iPRF targets. For follicles where DPC androgen receptor signalling has suppressed Wnt output, CAP provides an upstream Wnt stimulus that works around that suppression rather than through it. Nitric oxide-driven perifollicular angiogenesis from CAP also compensates for the attenuated anagen-phase vascular expansion in miniaturising follicles. These are non-redundant pathways to the same target, which is precisely why iPRF and CAP in combination address androgen-influenced follicle decline more completely than either alone.

, where the inflammatory or oxidative environment has become a secondary driver of DPC function impairment, provide the ECM and -reduction context that improves IGF-1 receptor pathway efficiency before growth factor delivery. In post-menopausal clients where the scalp environment has accumulated oxidative burden alongside the androgen-driven changes, polynucleotides as a preparatory step are particularly relevant.

Closing: What the Treatment Sequence Is Ultimately Trying to Do

What this protocol is working toward, understood through the SHBG lens, is this: the follicles most at risk from SHBG-driven androgen excess are those in the miniaturisation process, where DPC signalling has been progressively compromised but the follicle’s structural capacity for recovery is still intact. The window for meaningful intervention narrows as miniaturisation progresses and the DPC population shrinks. Treating early, before vellus conversion is complete, addresses follicles that still have the cellular machinery to respond. SHBG context helps identify those clients earlier: not by waiting for dramatic visible shedding, but by recognising the perimenopausal hormonal shift as a signal that the free androgen environment has already changed, whether or not total testosterone has moved.

References

  1. Brzozowska M, Lewiński A (2020). Changes of androgens levels in menopausal women. Prz Menopauzalny, 19(4), 151-154 .

  2. Kavanagh K, Espeland MA, Sutton-Tyrrell K, et al. (2013). Liver fat and SHBG affect insulin resistance in midlife women: the Study of Women’s Health Across the Nation (SWAN). Obesity (Silver Spring), 21(5), 1031-8 .

  3. Laurent MR, Hammond GL, Blokland M, et al. (2016). Sex hormone-binding globulin regulation of androgen bioactivity in vivo: validation of the free hormone hypothesis. Sci Rep, 6, 35539 .

  4. Narinx N, David K, Walravens J, et al. (2022). Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone in androgen physiology. Cell Mol Life Sci, 79(11), 543 .

Also Known As

  • sex hormone-binding globulin
  • SHBG

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