Excessive foam in a commercial bottled beer

I am wondering what are common causes of excessive foaming in a commercial beer?

The bottle of commercial beer foams excessively especially when the beer is cold. Gently pouring the beer onto the side of a pint glass will cause head to foam up almost the entire pint glass.

I bought this beer at a distance location from home (during a trip), so it did sat in the trunk of a car for ~6 hours (during summer). The beer was a 6 pack. The first 2 which i drank relatively soon after the drive didn't foam all that much. After a month in the fridge, I then noticed the excessive foaming. I finally opened the last bottle, which had sat in the fridge for 5+ months, and it still foams agressively.

Does anyone know the cause of this? This is purely for the interest of knowing what makes head in a beer. Would it be reasonable to suspect that slight spoilage could contribute to excessive head in beer?

Thanks

J

You shoulda drank em on the way home. LOL. Jk, if the beer doesn't taste bad, I wouldn't say spoilage. It could be over carbed.