We wear the mask that grins and lies,
It hides our cheeks and shades our eyes,—

The metaphorical “mask” in Dunbar’s poem represents the fact that in his post–Civil War American society, African Americans are forced to hide their distress as they struggle under racism and segregation. Dunbar writes that this mask conceals the “cheeks” and “eyes”—two parts of the face that commonly express emotion. The mask thus conceals any emotion the eyes might express, like sadness or fear; and since cheeks often flush with emotions like anger or embarrassment, it also conceals African Americans’ shame and frustration in their segregated communities. 

Nay, let them only see us, while
We wear the mask.

In order to not anger the white community, who want African Americans to remain “in their place” even after slavery has been abolished, African Americans must conceal their true feelings of anguish and frustration. They cannot allow themselves to be seen without this mask; they fear the consequences of appearing ungrateful or dissatisfied. 

We sing, but oh the clay is vile
Beneath our feet, and long the mile;

In addition to “wearing the mask” to conceal emotions, African Americans in this society also “sing” to produce the image of joy. They “sing”—despite the “long” and “vile” path of their life—to feign joy, just as their masks do. 

But let the world dream otherwise,
       We wear the mask!

In the last line of the poem, Dunbar finishes his refrain of “We wear the mask” with an exclamation mark, further emphasizing the fact that the smile African Americans appear to wear is merely a disguise. Despite the white world’s misconceptions and ignorance, Dunbar implies that African Americnas must continue to suppress their true emotions.