system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is high blood pressure bad for you (due to the damage to the arteries and blood vessels) but regular exercise, which also increases blood pressure, doesn't cause the same damage?
gpt
1. High blood pressure leads to enlargement of your heart (because it needs to pump harder in order to overcome the resistance of your narrowed/blocked/damaged arteries). This leads to all sorts of heart problems, particularly dilated cardiomyopathy. 

2. Exercise leads to a *transient* increase in blood pressure. People who exercise excessively tend to have larger hearts too (particularly left ventricular hypertrophy) and this also has the potential to cause problems, however, you would have to exercise *a lot* for this to happen. There are two key differences between transient high blood pressure from exercise, and high blood pressure from clogged vessels. Firstly, exercise only raises your blood pressure momentarily, however, the longer-term effect of exercise is reduced fat clogging your arteries leading to an overall reduced blood pressure for the majority of the time. The second difference is that in exercise whilst your heart needs to pump harder (to move more blood around), however, this is against low resistance. This process of pumping harder makes the heart stronger. By contrast, when you have high blood pressure your heart needs to pump harder *against resistance*, leading to dilatation which is far more problematic. Dilatation is like filling a balloon with water - the balloon expands, but it does not get stronger/more elastic. 

3. High blood pressure causes damage to the heart and the kidneys. However, high blood pressure also indicates clogged arteries and/or kidney disease (amongst many other things). These things that you have when you have high blood pressure cause damage too, damage somebody who exercises well does not have. 

Difficult, but great question!