The most common and most likely answer to this crossword clue is the 9 letter word SUNBONNET
I've seen this crossword clue in The Times
S
U
N
B
O
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T
More clues leading to the result SUNBONNET
Buddy explains!

The straight part
We know that "that prevents red faces" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that prevents red faces = sunbonnet.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 SUNBONNET mean?
SUNBONNET noun- A hat (bonnet) worn for protection from bright sunlight.