Question: According to [http://apps.tsa.dhs.gov](http://apps.tsa.dhs.gov/mytsa/cib_results.aspx?search=Liquid) it says the following:

> 
> **You may carry liquids, gels and aerosols in your carry-on bags only if
> they adhere to the 3-1-1 rule: containers must be 3.4 ounces or less;
> stored in a 1 quart/liter zip-top bag; 1 zip-top bag per person,
> placed in the screening bin. Larger amounts of non-medicinal liquids,
> gels, and aerosols must be placed in checked baggage.**
> 
> 
> Medically
> required liquids, such as baby formula and food, breast milk and
> medications are allowed in excess of 3.4 ounces in reasonable
> quantities for the flight. It is not necessary to place medically
> required liquids in a zip-top bag. However, you must tell the
> Transportation Security Officer that you have medically necessary
> liquids at the beginning of the screening checkpoint process.
> Medically required liquids will be subjected to additional screening
> that could include being asked to open the container. We recommend,
> but do not require, that medication be labeled to facilitate the
> security process. Many airports have designated lanes for families and
> individuals with items requiring additional assistance with screening.
> 
> 
> 

The problem is, I've been able to do this once (domestic), however the second time I had it taken away (international).

The time that I had it taken away was when I actually told the dude I had it in my bag, they removed it, kept it, and told me it was not allowed.

Is this up to the discretion of the TSA officer, or is it due to the fact I was in the international terminal versus the domestic terminal? I don't really see the difference.

Answer: 
You quote the TSA:

> 
> Medically required liquids, such as baby formula and food, breast milk and medications are allowed in excess of 3.4 ounces in reasonable quantities for the flight. 
> 
> 
> 

The key is "reasonable quantities for the flight." For most people, 3.4 ounces of contact lens solution is far more than would be needed for a single flight. If you need more contact lens solution than that for use at your destination, you are supposed to put it in your checked baggage. For longer trips, therefore, you would need two bottles: a small travel bottle for use on the plane and a larger bottle for use after you arrive at your destination.

I don't know why the TSA would have allowed you to take a larger bottle on the domestic flight. I can imagine that any of several reasons might apply. For example:

* The TSA officer may have been unfamiliar with contact lenses, and therefore unfamiliar with the amount of solution one typically needs to use.
* The TSA officer may have decided that you didn't represent a threat, and therefore may have exercised discretion (which may or may not have been in keeping with the rules) to allow you to retain the solution.
* Re-reading your question, I note that you don't say whether you actually discussed the contact lens solution with the officer when you were allowed to keep it. If you did not, they may simply not have noticed it. I've once or twice accidentally carried bottles of liquid through that the TSA screeners missed.
* If you *did* discuss the solution with the TSA, as I noted in my comment, it may just be that the TSA officer was not in the mood to argue, or that you are a particularly skilled negotiator. That's kind of frightening, but it's possible.

I do not know whether TSA rules allow laxer screening of domestic flights, but I doubt it.
I don't believe that security should have allowed you to carry the contact lens solution on board on either flight.

In December 1994, Ramzi Yousef smuggled nitroglycerin on board [Philippine Airlines flight 434](https://en.wikipedia.org/wiki/Philippine_Airlines_Flight_434) inside a bottle of contact lens solution, with other bomb parts concealed in his shoes, and assembled a bomb in the lavatory. When the bomb went off, one person died, another 10 were injured, and the plane almost didn't make it back as the bomb damaged some control cables needed to fly the airplane.

(This is the same Ramzi Yousef who bombed the World Trade Center in 1993.)

As a result of this and some similar plots which failed, carry-on liquid containers are restricted in size.

To ensure that you get through security, you should bring a small bottle for use during your flight, and a larger bottle in your checked baggage.