Three popular theories can be argued. The first, but least interesting is that its just genetics and its simply bound to happen when everone is blonde. The second and more complex theory begins when two magnetic fields on the suns surface collide which creates a solar flare. A solar flare bursts away from the suns surface and carries through space as magnetic energy waves called Solar Wind. When Solar Wind reaches the Earth it is buffetted by the upper atmosphere and they are pushed poleward. This Phenomena can often be seen at night time and referred to as Northern or Southern Lights. Unfortunately, the Swedish use so many ChloroFluroCarbons (CFC's) in an attempt to erradicate mosquitoes with insect spray, remove the squeaky noises from their door hinges with WD40, and give their hair more lift with peroxide spray, the Earths atmoshere above has been somewhat weakened and diminished which gives the Solar Wind a chance to bleach hair.
The third and most poplular theory is quoted from a famous Swedish Scientist Gustav Hienrick "...well...just 'cause. Somethings just aren't meant to be explained so why bother." Many of Gustavs theories have been shunned by his piers but Gustav argues that most science is actually irrelevant and really people should just take a Snus and chill out.
A fourth and less discussed theory is that many simply bleach their own hair. It is seldom discussed but most likely the most reasonable explanation.
I am currently in Sweden and enjoying the hospitality of a Swedish friend I met in China. I am in Gothenborg and have participated in many swedish traditions since I arrived. Taken a Sauna and swim at a lake, rock hopping on smaller islands , eaten traditional Swedish Cuisine, tried a snus, and driven on the right hand side of the road.
