À fleur de peau

Here is an elegant and visual expression that will impress any audience.  Être à fleur de peau is used figuratively to describe a person with heightened sensitivity.  It can be used as a semi-compliment to characterize someone who is easily moved by, let's say, beauty or kindness.  Or it may depict a person who is thin-skinned, easily emotional, maybe a tad touchy.  It can also portray someone who is just a bundle of nerves and quick to overreact.  Depending on the context, you could even say that they make a mountain of a molehill.

Fleur is French for flower and peau means skin.  If you wonder what a flower is doing here, you might be surprised to know that fleur can also mean on the surface of, when used with the preposition à.  Literally, à fleur de peau translates to: on the surface of the skin.

Indeed, the meaning of the expression is based on the rather poetic image of what is on the surface of the skin, what transpires, or even what is easily awakened, as if by epidermal reaction.

It is often associated with nerves, as in avoir les nerfs à fleur de peau (to be on edge) and sensitivity, as in avoir une sensibilité à fleur de peau (to be hypersensitive.)

Origin

Not surprisingly, the first written records of the phrase à fleur de come from 14th century works ... of botany!  The form mostly used at the time was à fleur de terre (earth) and described what is found close to the surface of the earth.  Now, what is found right there close to the ground?  Flowers, precisely.

Over time, with the natural evolution of the language, the expression became popular and was applied to other areas, taking on the general meaning of on the level of.

For example, in La Nausée by JP Sartre, we find the expression à fleur d'eau:  Une flaque de lumière au loin, c'était la mer à marée basse. Quelques écueils à fleur d'eau trouaient de leurs têtes cette surface de clarté.
A puddle of light in the distance was the sea at low tide. A few reefs on the surface of the water pierced this surface of light with their heads.

Among the same lines, cooks among us will have also heard of la fleur de sel, which comes from floating salt crystals skimmed from the surface of seawater as it evaporates - and used as a finishing salt to flavor and garnish food.

Examples

Changeons de sujet; les émotions sont trop à fleur de peau.  
Let's change topic; emotions are running too high.

Vivez une expérience unique: sentez les Caraïbes à fleur de peau.
Live a unique experience: feel the Caribbean upclose and personal.

Il est normal d'être à fleur de peau après un tel bouleversement!
It's normal to be on edge after such an upheaval!