Glossary
The terms on this site, in plain language
Short definitions of the medical words that appear on our pages. They explain what each thing is; they do not replace a medical evaluation or promise an outcome.
Biological age and lab tests
- Chronological age
- The years since you were born.
- It is the calendar figure, with no interpretation. It serves as the reference for comparing a biomarker-based estimate.
- Related: Biological age
- Biological age
- A statistical estimate that combines several biomarkers in a model; it guides, it does not diagnose.
- It depends on the model and the data it was built from. An estimate lower than your age does not mean you have fewer years or have grown younger. We do not publish “reversal” figures.
- Related: Chronological age · Biomarker
- Biomarker
- A measurement from the body, usually blood, that tells us how a system is working.
- A single biomarker says little on its own: it is read alongside your history, other results and how it changes over time.
- Related: Reference range · Biological age
- Reference range
- The interval where most of a reference population falls.
- It usually covers 95% of that population, so it varies between laboratories. Being inside it does not mean zero risk, and being slightly outside it does not turn a healthy person into a patient. That is why we also look at trends and history.
- Related: Trend
- Trend
- How the same marker changes across several measurements.
- It usually says more than a single value, because one test captures a single moment.
- Related: Reference range
- HbA1c (glycated hemoglobin)
- The share of hemoglobin with glucose attached; it summarizes about three months.
- Fasting glucose is a snapshot; HbA1c is an average, because red blood cells turn over in about 120 days. That is why we use it to follow a change at 90 days. If red blood cells live shorter than usual, the number shifts.
- Related: Fasting insulin
- Fasting insulin
- The hormone that helps store glucose, measured while fasting.
- Early on, the pancreas can compensate and keep glucose normal at the cost of more insulin. That is why it is read as a trend and in clinical context, with no universal cutoff.
- Related: HOMA-IR · HbA1c (glycated hemoglobin)
- HOMA-IR
- A calculation from fasting glucose and insulin that approximates insulin sensitivity.
- It is a guide, not a diagnosis, and it is read together with the other markers.
- Related: Fasting insulin
- ApoB (apolipoprotein B)
- The protein carried by each particle able to take cholesterol into the arteries.
- If LDL measures the cargo, ApoB counts the trucks: there is one ApoB per particle. It is read alongside your cardiovascular risk, your history and clinical-guideline targets.
- Related: Lp(a) · Cardiovascular risk
- Lp(a)
- A lipoprotein determined mostly by genetics.
- Because it barely changes over a lifetime, it is measured once in adulthood and not repeated at 90 days.
- Related: ApoB (apolipoprotein B)
- hs-CRP
- A blood signal of inflammation.
- It rises with an infection, an injury or even hard training. Those causes are ruled out before it is interpreted.
- Complete blood count (CBC)
- The count of red cells, white cells and platelets.
- A single abnormal value may mean nothing; a persistent change calls for medical follow-up.
- Related: Metabolic panel and eGFR
- Metabolic panel and eGFR
- A test of kidney and liver function and electrolytes.
- eGFR estimates how well your kidneys filter, based on creatinine. If something is abnormal, we look for the cause.
- Related: Complete blood count (CBC)
- Cardiovascular risk
- The estimated probability of a heart or blood-vessel event.
- It combines markers such as ApoB with blood pressure, history and habits. No single test sums it up.
- Related: ApoB (apolipoprotein B)
Recovery
- Hyperbaric oxygen therapy (HBOT)
- Breathing oxygen at higher-than-sea-level pressure inside a chamber.
- The FDA clears the chamber for specific indications, such as selected wounds or compromised grafts; other uses are being studied. Pressure and number of sessions are part of the indication.
- Related: Adjunctive therapy
- Adjunctive therapy
- A treatment added to the one your physician prescribed, not a replacement.
- For wounds or after surgery, adjunctive therapy is coordinated with the plan of the team treating you.
- Related: Hyperbaric oxygen therapy (HBOT) · Photobiomodulation (red light)
- Photobiomodulation (red light)
- The use of low-energy red and near-infrared light to influence cellular processes, without heat or ultraviolet.
- The light acts mostly at the surface and fades with depth. More light or more time does not mean more effect: too much can make the result worse.
- Related: Wavelength (nm) · Biphasic response · “FDA cleared” vs. “FDA approved”
- Wavelength (nm)
- The “color” of light, measured in nanometers.
- It decides how far the light reaches: red stays closer to the surface and near-infrared goes a little deeper. Far infrared no longer acts as light but as heat.
- Related: Photobiomodulation (red light) · Far infrared
- Biphasic response
- Too little may do nothing, and too much can make it worse.
- That is why more minutes or more power do not mean more benefit, and distance and time are part of the dose.
- Related: Photobiomodulation (red light)
- “FDA cleared” vs. “FDA approved”
- Two different FDA pathways: “cleared” is not “approved.”
- A “cleared” device (510(k) pathway) is authorized because it is equivalent to one already authorized, for the indications on its label. “Approved” is the approval of a drug or a high-risk device after it has shown safety and effectiveness. A lot of advertising uses the first so it sounds like the second.
- Related: Photobiomodulation (red light) · Hyperbaric oxygen therapy (HBOT)
- Observational study
- A study that watches who does what and what happens, without random assignment.
- It shows association, not causation. The large sauna studies compared frequent with weekly use of traditional Finnish sauna, not infrared.
- Related: Far infrared
- Far infrared
- Radiation that warms the body without heating the air much.
- It is what the sauna capsule uses. It is heat, not photobiomodulation, and the evidence for traditional sauna does not simply carry over to infrared.
- Related: Observational study · Wavelength (nm)
- Cryosauna (whole-body cryotherapy)
- A brief exposure to very cold, dry air inside a cabin.
- Water draws heat away far faster than air; that is why the cabin is tolerated with dry, protected skin. It is not water immersion and does not share its evidence.
- Related: Vasoconstriction
- Vasoconstriction
- The narrowing of skin blood vessels to keep the body's core warm.
- It is the body's response to cold, the opposite of sauna. It explains why hands and feet hurt and why Raynaud's is an exclusion.
- Related: Cryosauna (whole-body cryotherapy)
Medical aesthetics
- Botulinum toxin
- A medication that temporarily reduces activity in the muscle where it is injected.
- It blocks the signal the nerve sends the muscle to contract. It softens certain expression lines, the ones that appear when you move your face; the effect is temporary and reversible.
- Related: Off-label use · Informed consent
- Hyaluronic acid
- A water-retaining molecule; as a filler it restores volume and breaks down over time.
- Each filler is approved for specific areas. Duration varies by product, area and person. In topical skincare it only hydrates the surface: these are different uses.
- Related: Botulinum toxin
- Off-label use
- Using an approved medication for an indication or area not listed on its label.
- It is legal in medical practice, with informed consent, but the FDA has not approved it for that use. Your clinician will tell you whether what they propose is on-label or off-label.
- Related: Botulinum toxin · Informed consent
- Informed consent
- The agreement you sign after learning the risks, benefits and alternatives.
- It is a conversation before it is a form. In aesthetics it is specific to the procedure and separate from photo consent.
- Related: Off-label use
IV therapy
- Bioavailability
- The share of a substance that reaches the bloodstream.
- By vein it is nearly complete, but reaching the blood is not entering the cell and does not prove a benefit. IV therapy is indicated when there is a documented need.
- Related: NAD+
- NAD+
- A molecule involved in cellular metabolism.
- Infusing it has not been shown to extend life or reverse aging. More in the blood does not mean more activity in the cell.
- Related: Bioavailability
GLP-1
- GLP-1 receptor agonist
- A medication that mimics a hormone your gut already releases when you eat, but lasts much longer.
- Your natural GLP-1 lasts minutes; the medication is modified to last days. It acts on brain areas that regulate appetite and slows stomach emptying. Each product has its own approved indications: some for weight, others only for type 2 diabetes.
- Related: BMI (body mass index) · Lean mass · Compounded version
- BMI (body mass index)
- Your weight in kilograms divided by your height in meters squared.
- In the trials of these medications, obesity was defined as a BMI of 30 or more, or 27 or more with a related condition. It is a selection criterion, not a measure of your health on its own.
- Related: GLP-1 receptor agonist
- Lean mass
- Everything that is not fat: muscle, water, bone and organs.
- Any weight loss, with or without medication, takes some lean mass with it, and lean mass is not the same as muscle. That is why the plan adds protein and strength work to help preserve it, and we measure your strength, not just your weight.
- Related: GLP-1 receptor agonist
- Compounded version
- A pharmacy-made preparation, not approved or reviewed by the FDA.
- The FDA does not review their safety, effectiveness or quality before they are sold. Fenix prescribes FDA-approved medications.
- Related: GLP-1 receptor agonist
- Medullary thyroid carcinoma and MEN 2
- A rare thyroid cancer and a rare inherited syndrome that predisposes to endocrine tumors.
- If you or anyone in your family has had it, these medications are not used: it is a contraindication on their label.
- Related: GLP-1 receptor agonist