What causes an abcess?

My lesson horse came up lame a few days after my last lesson. My instructor told me that the vet & farrier came out & he had abcesses in both front feet.
I understand what an abcess is but what causes them? I was always taught that the hoof was much like our own finger nails, so how do you get in an infection in that?

When something penetrates the bottom of the hoof, like a nail or bit of barbed wire or even a stone, the infection can get into the hoof. Sometimes the foreign object works its way up and the infection forms around it, and sometimes the infection just comes in through the wound.

I have to say though, I've never come acros a horse with both front feet getting abscesss at the same time! Hope he's better soon

Hoof horn is indeed like fingernails. It can indeed get infected. That's called 'seedy toe' or 'whiteline disease'. Abscesses however are when an infection or injury affects the live tissue - the corium underneath the horn. You can think of it as a pimple or a blood blister... under your fingernail - ouch!

Abscesses can come about from stone bruises to thin soles & frogs, injury to the wall or coronary border, laminitis, separation, cracks, infection(seedy toe), overlong &/or imbalanced walls, contracted hooves, etc. Sometimes they can come about from puncture wounds.

As you can see, abscesses can be a 'one off' accidental type affair or they can signify major underlying issues. If your horse is lame in both feet or 'prone' to abscesses, it's likely there's something going wrong that is causing them.

Where abouts were the abscesses & more details needed if you want any specific opinions on them.