Why does God "allow" suffering?

what is suffering? what causes it?

well first of all, let's start somewhere near the beginning...

"17 And unto Adam he said, Because thou hast hearkened unto the voice of thy wife, and hast eaten of the tree, of which I commanded thee, saying, Thou shalt not eat of it: cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life;" Genesis 3:17

so the earth became cursed because of Adam's sin, all of creation and everyone that was to be born was now punished because of the sin of Adam.
This is where suffering comes from...sin.
The original sin caused all disease and any other "natural" affliction.
But it's the sinfulness of all mankind that causes much more suffering. 
Greed is the reason for people starving. 
Lust is cause for abortion, which is murder.
Hatred is the cause of all sorts of evil deeds.
why does God "allow" this?
In the old testament He didn't always, 
for example when man became overbearingly evil and sinful,
God caused the flood and just spared Noah and his family
When Sodom and Gomorrah became a place of evil and sinful behavior...

(let me stop here to just say that even though homosexuality is a sin, that this town was not just people "dating" the same gender, those people where rapists and child molesters. Only one family, which was Lot's, were not doing these things. Every person in town was taking part in orgies and raping others. They even tried to rape the Angels that God sent to get Lot and his family out) 
God destroyed those places...

there are other examples of this, 
but the question presented isn't even valid, God doesn't "allow" suffering.
Suffering happens because of sin... God isn't allowing suffering, He's extending mercy.

mercy to people you love...
 you could have a teenage boy in your family that harasses young girls he goes to school with, those girls are suffering

you could have a racist uncle who yells at people of a different color, those people are suffering

your mom could be someone that yells at every service worker she encounters when she shops somewhere, they are suffering 

your brother could be a rapist and you don't know about it, which causes the victims to suffer

your uncle could be beating his wife, causing her suffering

your child could be selling or using drugs
they could be beating up children for money or enjoyment 

you could get the wrong attitude with someone around you and yell at them, making them suffer 

you could make fun of people thinking they can't hear you, but they do, making them suffer

those people you love, 
and even yourself, 
we all are at some points the cause of someone else's suffering, 
I know that I have been...

God "allows" suffering, because He loves everyone, and since He sent His Son Jesus to die for our sins, we can be in heaven if we accept Jesus Christ as our personal Savior...

but this earth is still cursed, we still live inside a sinful flesh, and we still live among sinners... 
stop asking why God allows suffering and start being thankful that He extends mercy to us, the ones that cause it