There are misconceptions about what shower filters do. Shower filters employ KDF media that converts the chlorine molecule (Cl2) to chloride ions (CL-). Chlorine is a poisonous gas or liquid, considered one of the most toxic on earth, while chloride is harmless at low levels (high levels of anything can be a problem). So a shower filter removes a high level of chlorine, as much as 90%.
Shower filters do not remove the carcinogenc byproducts of chlorine in your shower water. When chlorine is added to water for the purpose of killing bacteria it interacts with organic material in the water and forms a number of carcinogenic byproducts including the Trihalomethanes and Haloacetic acids. These are groups of compounds known as volatile organics. These groups of compounds have been determined to be linked to cancer and are regulated as a result by EPA. These chlorine byproducts are far more dangerous to you than chlorine. There are other unregulated byproducts which are also carcinogenic.
Shower filters also do not remove chloramines. Some filter companies make the claim that they do but I do not believe them. They may reduce chloramines slightly. Chloramine is a combination of chlorine and ammonia which is increasingly used as a replacement or in combination with chlorine. Chloramine produces lower levels of Trihalomethanes and Haloacetic acids but produces other byproducts which are equally dangerous.
Some shower filters use additional media and make additional removal claims but those are by and large baloney.
So when you use a shower filter you reduce chlorine by 90% but do nothing to address the other carcinogenic compounds in your shower water.
Whole house water filters remove chlorine, chloramine, and their carcinogenic byproducts as well as other volatile organic compounds like pesticides. When chloramines are present in water I employ a particular type of carbon, known as catalytic carbon, that removes chloramine. Common granular activated carbon does not remove chloramine. It is my experience that whole house water filters with catalytic carbon do not remove 100% of chloramine. Hence I also recommend a kitchen water filter when chloramines are present. The kitchen water filter will remove the last bit of chloramine to provide healthy drinking water.
This is the reason that a $50 or $100 shower filter does not compare in effectiveness to a $2000 whole house water filter. If you want healthy water for bathing then a whole house water filter is the way to accomplish your objective. I thought it would be useful to articulate this difference for the many people who purchase shower filters thinking that they are no showering in healthy water.