Why do teenagers send nude pictures?

They do it so people want them.

It's a natural human instinct.

Ironically it can be sexier to keep your clothes on; teens won't necessarily understand this yet though. I think if you just show your whole body then there's nothing left for them to 'discover'.

Sorry whats the dufference...?

Adults usually feel more in control. Adults in their twenties have a fully developed mind and are used to a whole array of emotions. Adults generally have greater control over themselves in regards to pressure, thinking of possible consequences and the right decision. The human mind isn't fully developed until around 23. Obviously the difference between a young 18 year old and someone who is nearly 18 is minor but the difference between a 14-15 year old and a 25 year old is massive.

Personally at 29 I feel much less in control when it comes to sexy things than I did at 11.

There are more decision paths and the consequences have got bigger. When I was 11 my woman wasn't asking about co-habiting, or how many kids I want or where I saw my career headed. As you get older thigns like money kick into play too which is one of the better ways to coerse someone.

I pretty seriously doubt the ability to control yourself under pressure changes at all with age, where the couple involved are of similar age. Or perhaps I'm the opposite of everyone else who knows.

It's two different types of pressures. I'm talking about the peer pressure as you are growing up; the new feelings you feel about the opposite sex as you've never experienced them before, the naivety kids have that the world is all friendly, the ignorance of the dangers of the internet, the first crush, the first kiss, the first time you seem a genital belonging to someone else, the butterflies in your stomach when something sexual crops up, the first orgasm etc...
All affect the ability to think straight over sending a nude photo. It's like being alone in a foreign city, where you don't speak the language and it's the middle of the night. You feel vulnerable. That's how children are but they still end up sending nudes.

In your twenties seeing someone nude is nothing new, the first kiss, the excitement of the first love is all over. You now have adult world worries. However, despite your adult worries and the pressures of finances and kids, you have the ability and life experience to think through the consequences of sending a nude, how it could end up permeability on the internet, how one day in the future it could be used against you etc... It takes adults longer to trust someone usually. Children trust anyone promising them ice cream.