What are surfactants?
Surfactants are an ingredient typically found in shampoos and conditioners. You may have seen the word thrown about curly hair forums and websites, but it's important to know that not all surfactants are the same. The surfactants typically found in shampoos are intended to clean and the surfactants found in conditioner are intended to deposit. The key difference between the two types is the size (or length) and the charge - negative in shampoo and positive in conditioner.
All surfactants are not the same.
Surfactants in shampoos include SLS, SLES, ALS and their purpose is to remove oil and wash hair. Surfactants in conditioners include behentrimonium chloride, behentrimonium methosulfate and stearamidopropropyl which are designed to deposit onto hair, smooth the cuticle and create softness. This image from NaturalHavenBloom explains it visually:
So now to get to the answer that you are most likely here for.
Are surfactants bad for your hair?
You probably won't like this answer, but yes and no. This is another one of those trial and error, see how it works for you personally kind of things. If a shampoo formulation only had water and a surfactant in it such as SLS then yes- it would irritate your skin and most likely dry your hair out. However, in most formulations, there are co-surfactants present, such as fatty alcohols, present which help to balance the formula and drying effects of the surfactants. Also, most formulations contain additives such as moisturizing oils and conditi oning polymers that can help prevent damage to the hair.