Testosterone gel (Testogel) is external testosterone. It is a gel that is applied on the arm, and is absorbed through the skin. External testosterone is an effective way to increase testosterone levels since it directly replaces your body's lost testosterone with the right levels of testosterone. This treatment may suppress the production of sperm, which may be irreversible after long-term use, and so it might impact your fertility. This treatment needs to be taken long-term. Should you stop treatment, there is a risk that you will not recover your baseline testosterone levels, and it may lead to testicular shrinkage.