Your underlying genetic skin type doesn't change, but the practical, observed way your skin behaves can shift somewhat with age, season, and accumulated sun exposure.
The genetic baseline is fixed
The core melanin-production capacity that defines your Fitzpatrick type is set genetically and doesn't change throughout life — this is the formal, clinical definition of the scale.
What can shift practically
Skin can appear to tan more easily after repeated seasonal exposure (a mild practical adaptation), and can also become more sun-sensitive with age or certain medications — which is why re-checking your practical sun sensitivity periodically is reasonable, even if your formal type doesn't change.
Why apps re-scan periodically
A fresh scan accounts for seasonal skin changes, recent sun exposure history, and any medication changes that affect photosensitivity — useful even for someone who's confident in their general skin type.
Do certain medications change how easily you burn?
Yes — photosensitizing medications (certain antibiotics, acne treatments, and others) can significantly increase sun sensitivity regardless of your baseline Fitzpatrick type, which is why checking with a pharmacist or doctor about any new medication's sun-sensitivity warning matters.