The most common and most likely answer to this crossword clue is the 4 plus 2 plus 7 letter word NOLI ME TANGERE
I've seen this crossword clue in The Guardian
N
O
L
I
M
E
T
A
N
G
E
R
E
Buddy explains!

The straight part
We know that "balsam? Leave well alone!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case balsam? leave well alone! = noli me tangere.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NOLI ME TANGERE mean?
NOLI ME TANGERE noun- Lupus.
- A growth or cancer on the face.
- Any of various plants that, when ripe, discharge their seeds when touched. Especially:
- A picture showing Jesus appearing to Mary Magdalene.
- A warning to avoid.
- Something to be avoided, such as a taboo topic or painful experience.