The same hour in the sun can leave one person golden and another badly burned — the difference comes down to how much melanin their skin produces and how quickly.
Melanin is the core variable
Melanin is the pigment that darkens in response to UV exposure and also absorbs UV radiation, providing some natural protection — skin types that produce more melanin, more quickly, tan more readily and burn less easily.
Genetics set the baseline
How much melanin your skin can produce, and how fast, is largely genetically determined — this is exactly what the Fitzpatrick scale is measuring, and it's why the same sun exposure genuinely does produce different results across skin types.
Why this matters for a routine
A one-size-fits-all sun exposure recommendation ignores this real biological variation — which is why matching SPF and exposure time to actual skin type, rather than a generic rule, is the more accurate approach.
Can you increase how much melanin your skin produces?
Not meaningfully through lifestyle choices — melanin production capacity is largely genetic; gradual sun exposure builds some additional pigment (a tan) but doesn't change your underlying baseline skin type.