There's no solid answer behind the steady rise in average breast size, but there are some theories.
Some fashion designers believe that the increase in average breast size is a result of the garment industry. Many clothing manufacturers inflate or deflate sizes according to the times. As all women know, different brands of shoes and clothing fit differently. There's a big difference in a size 10 from two different companies. And as larger breasts have become more fashionable, possibly C cups have been getting smaller so more women can be proud to have a larger than average size.
Some sociologists point to the general weight gain among Americans as the cause of the increase in average breast size. Bigger people, the remind us, tend to have bigger breasts. And as obesity reaches epidemic proportions, the breasts of overweight women keep pace with the rest of them.
A final, and far more terrifying, explanation is that of excessive estrogens in the environment. Due to industrial pollution and widespread use of oral contraceptives, there are high levels of estrogens found in water in many places. In some rivers, fish are dying out because there's so much estrogen in the water that all the fish are born female. In this scenario, average breast size is growing due to this hormonal pollution.
On the other hand, an increasingly safe and effective set of natural breast enlargement solutions has been available for quite some time. We are certain that a significant portion of the increase in average breast size is at least partially due to the widespread availability of reliable breast enlargement solutions.