What causes increase in DHT levels?

Science lesson!

DHT is formed by an enzyme called 5-alpha reductase. For this explanation, lets call it george.

So george is in your prostate making testosterone into DHT all your life. Its not really a problem, but then you get old. Your prostate grows (as happens to most men as they age) and as your prostate, george gets extra ambitious, and makes more DHT.

As your prostate grows, DHT levels will go up. There are drugs to shrink your prostate though! So talk to your doctor!