My food grade is about 2 yrs old now and still 'fizzes'.
It needs to be kept in the fridge with the lid loose.
I always use HP on cotton buds in my ears for a cold.
I do sometimes use it for my teeth
but the fridge is downstairs and I clean my teeth upstairs.
I really need to sort my life that really is no excuse
Personally I wouldn't use anything other than food grade internally
and really think that if I am using it externally it is going to
go in through the skin.
It is illegal to put 35% in the post in UK
(infact the people I used to buy from had to stop selling any
so now I have to get mine from Ireland.)
They used to have theirs delivered by special 'truck' of some sort.
Then they had to treat it to make it 6% food grade to sell to the public.