Much of the poems effectiveness comes from the use of comparisons made mostly by similes. Each simile represents a possible effect of a dream being put off. The first asks if a dream dries up "like a raisin in the sun." The dream may become shriveled and brown and uninteresting like a dry raisin, baking in the sun's heat. The second asks if it festers "like a sore" and then that sore runs. The dream may eventually turn into something harmful to oneself as an infected sore harms the body. The dream may then "stink like rotten meat." The dream you held so dear becomes something repulsive enough to cause you to gag. It may also "crust and sugar over" forming a sweet barrier around the issue your dream pursues. In the final simile, the dream may "[sag] like a heavy load." weighing you down, causing you no longer to have the strength to chase it.
What packs the punch though, is that after all the similes, "AP" Langston Hughes attacks the subject with a succinct metaphor asking if the dream explodes. An explosion is never good and carries with it connotations of violence and destruction. When put in the context of the time and author, it could refer to Langston Hughes believing civil rights will only come after violence takes its course.
