Dark patches on neck.

My daughter is almost 15 and she has these dark patches on the back of her neck. I've been reading around and I've heard it might be signs of diabetes, so I'm really worried,  plus she is a bit overweight, but I'm helping her with that.
She's had this for a few years now, but she would like to lose the dark discoloring on her neck before school starts. I've heard the Alpha Hydroxy cream might lighten it up a bit.
Any other suggestions?

[octopus]

Does she have any patches anywhere else??
I have had this on the back of my neck and was told that it was a fungal infection called pittyrisis versicolor (not sure of the spelling) I was advised to wash in shampoo called selsun.
When your daughter goes out in the sun does she also get patches of skin which don't tan as this is also a sign of the infection.

[biteme916]

Honey, it is a sign of diabetes. I've had it since I was a little girl and I was diagnosed with diabetes when I was 15. I was overweight. Not only were my patches on my neck, but also my armpit and inner thigh area. I forgot what the dark patches are called but my doctor explained to me that it is caused by the sugar sitting around ur blood streams. the lymph nodes on your neck, armpits and groin area absorb really easily. So the sugar is absorbed to your head and is encrusted on your neck. It sounds sick, but it can be treated. Glucophage helps lose weight and eating less sugar/carbohydrates = no dark patches.