Dear Folks,
I have often heard it said that "80% of your lifetime sun exposure is before your 18th birthday". I wonder where this figure comes from? I don't believe it:
If we assume that childhood is from 0 to your 18th birthday, you have 18 years maximum for sun exposure during the childhood years. But, the first 3 years or so you won't be outside that much, therefore let us say that we have 15 good skin-frying years. There are 24 hours in a day, but only 12 daylight hours. Many of these will be spent inside in school, etc. So, as a generous guess, you might have 8 hours a day, 7 days a week
to cook yourself. 8x365x15=43,800 total frying hours.
Now, as an adult let us say you live until age 78 to give us the round number of 60 adult years: 78-18=60. You get an average of 19 hours a week sun exposure year round as an adult (from: Sunscreen in winter? No question about it:. Source: Prevention (Emmaus, Pa.). v. 51 no2, Feb. 1999, p. 70. Mooney, Linda.)
So, 19x52(weeks a year)x60 equals 59,280 total adult frying hours.
If we add the adult and child hours we get 59,280+43,800= 103,080 lifetime hours. The 43,800 children hours represent 43,800/103,080= 0.4249x100= 42.49% of the total.
If we assume that a child's skin is somewhat more vulnerable than an adults (say by a factor of two?). Then 43,800x2= 87,600 childhood hours. And let us further assume that you don't care after age 60 about your skin. Therefore, the adult hours would be 19x52x42=41,496. With the equivalent damage total hours then being 87,600+41,496=129,096 hours.
Therefore, on the rather generous assumptions that (1) the child is outside 56 hours a week 52 weeks a year, and (2) a child's skin (on average over the 15 years) is twice as vulnerable as an adult's, and (3) your romantic life ends at 60; then the childhood percentage of your damage is 87,600/129,096=0.6786, which is about 68% of the total.
Best Wishes,
Charles78
cdewitt@uiuc.edu