It's one of the most common sources of frustration in online reviews: one person raves that a device changed their life, another says it did nothing, and both are describing the same product used correctly. Genetics is usually the biggest hidden variable.
Follicle Density Varies Enormously by Person
The number of hair follicles per square inch of skin is largely genetically determined and varies significantly between individuals, independent of hair color or skin tone. Someone with naturally higher follicle density in a treatment area will have more hair to treat and may perceive slower visible thinning simply because there's more total hair, even if the percentage reduction per session is identical to someone with lower density.
Hair Growth Cycle Timing Is Individual
As covered in our guide to IPL session timelines, treatment only affects hair in the active growth (anagen) phase, and only 20-30% of hair is typically in this phase at any given time. But that percentage, and the length of each growth phase, varies by individual and by body area based on genetics — some people naturally cycle a higher percentage of hair through active growth at once, which can mean faster visible results from the same treatment schedule.
Hormone Receptor Sensitivity
Two people with identical circulating hormone levels can have genetically different follicle sensitivity to those hormones. This is part of why hirsutism (excess hair growth) can run in families independent of measured hormone levels — the follicles themselves are more responsive, not necessarily exposed to more hormone. This same variation affects how persistently hair regrows after treatment, independent of the device used.
Melanin Type and Concentration
Beyond the broad hair-color categories covered in our melanin guide, there's meaningful genetic variation in exactly how much eumelanin or pheomelanin any individual's hair contains within the same general color category. Two people who both have "dark brown hair" can have somewhat different melanin concentrations, which can produce somewhat different IPL absorption and results even when every other variable (skin tone, device, technique) is matched.
Regional and Ethnic Variation in Hair Characteristics
Hair diameter, curl pattern, and density can vary by ethnic background due to genuine genetic variation in hair follicle shape and structure. Curlier, coarser hair types can sometimes have follicles angled differently in the skin, which some manufacturers and dermatologists note may affect how consistently light-based energy reaches the full follicle depth — an area where individual results legitimately vary more than marketing claims typically acknowledge.
What This Means for Your Expectations
The practical takeaway isn't that any of these factors make treatment pointless — it's that comparing your results to a stranger's online review, rather than to the general published timeline (3-4 sessions for initial visible change, 3-4 months for substantial reduction), sets up an unfair comparison. Your own hair and skin genetics are the honest baseline to track progress against, not someone else's.
Bottom Line
Follicle density, hair cycle timing, hormone sensitivity, and melanin concentration all vary genetically between individuals, which is why identical devices used identically can produce different-feeling results for different people. Track your own progress against the general session timeline rather than against other people's individual experiences.