A 20 minute shower is considered too long by experts.
Taking a 20 minute shower could dry out your skin and remove too much of the natural skin oils.
However some people are just fine taking a 20 minute shower but for most people a 10 minute shower is more than enough time in the shower to get clean.
For some people anything over 10 minutes is considered too long for a shower but some people are just fine taking showers longer than 10 minutes.
I sometimes myself will take 20 minute showers when I get really dirty from working outside and then some days I just take a 10 minute shower which is enough.
Many experts would agree that anything more than 10 minutes is too much.
Make sure that you keep your shower time between five to ten minutes.
While it is tempting to stay under the shower for a long time, this will cause some health problems and will also waste a lot of water.