Why do we lose our carefully built up tan in a matter of a dozen weeks?

Well, you’re only changing the pigment in outermost layer of the epidermis. As those cells slough off and are replaced, your original skin tone comes back if you aren’t maintaining the tanning routine.

Exfoliation.

Us northern europeans are a pasty lot, just reverting to type.

Ah, it is that simple?!
Thank you both!
And @ucme too.

Exfoliation, and when you tan, you’re in the sun for a very long period of time. Once you’re out of the sun, the tan fades away.

Use it or lose it. You might think it’s attractive, but it’s really there to protect you from the sun. If you no longer need protection, you don’t keep building it up – and as they said up there, exfoliation ensues.

@laureth is right , use it up while you can.

You see dead people?? ;)

I have the opposite problem——I can’t seem to get rid of my tan! Why some people want to sit out in the hot sun to get a darker complexion I will never understand, and once they lose that tan through dead skin cells sloughing off, they are dissatisfied with their light skin.

I wish I could exfoliate to get rid of some of my golden complexion, but I guess it’s because my melanin is deeper and more concentrated, and not in the upper layers like @Blueroses said.

My wife and two little girls have very fair, sensitive complexions, and they burn easily out in the sun. If I go out in harsh sun for just half an hour, I get darker. And it takes quite a long time for me to get rid of my “extra tan”. Argh. I wish my daughters had inherited some of my “tan”—-to protect them from the summer sun, but apparently they got their lovely delicate skin from their mother.

So I think genetics has a lot to do with how long you can acquire and maintain a tan too.