Is 100% Deet dangerous?

According to the EPA, the answer is "No." (see http://www2.epa.gov/insect-repellents/deet ). Of course, all absolute claims should be taken with a grain of salt. And the state of NY has put out what seems to be a bit more reasoned assessment ( https://www.health.ny.gov/publications/2737/ ). That said, I have used (and continue to use) as close to 100% DEET products as I could find for over 40 years (30 years active duty infantry, 9 years in a wildlife agency, years of backpacking/hiking) and have developed no external or internal health issues. I use this because 1) many areas I operated in (Alaska, Thailand, Honduras, southern United States, Haiti, Panama, etc.) were almost literally unlivable if you couldn't ward off the insects and 2) because even more areas include insect-borne disease (Malaria, Dengue, West Nile, etc.). West Nile Virus activity exists in all but 6 of the lower 48 states and Dengue Fever (or its vector mosquito) is confirmed in Florida, Texas, Arizona, California and Hawaii. Lyme Disease and Encephalitis are also insect-borne diseases. As global warming evolves, other previously tropical insect-borne diseases will probably show up in the US. This is a cost-benefit analysis only you can do for you and your family. My answer rather arrogantly assumes you are talking about using this in the United States. If you are living/operating in more tropical areas outside the US, then it is really a matter of what type of personal insect control you are going to use, not whether to do so. Hope this at least helps reduce the ambiguity.

Is this an aerosol or just a spray? Need to know if this is allowed in the bags for international travel please?

This is a spray. It is not a pressurized container. The product works very well. It takes very little bug juice to give you protection. I spray a little bit in the palm of my hand, then rub my hands together to give them a coating of the repellent. I then rub the areas I want to protect with my repellent coated hands. I may do this a couple of times a day based on how much I am sweating. Make sure you don't get it in your eyes or nose. This does irritate those areas.

What does it smell like?

It doesn't smell like anything thank heavens.

Repellents with up to 30% DEET are safe for kids over 2 months old. Over 30% DEET doesn't protect any better, but does last longer. So get something with 30% DEET and reapply every 2 hours.