Because you're worth it.
"Really, other than their hair, the Kazon aren't too scary."
on Star Trek: Voyager
When humanoid aliens on TV have hair, it almost always falls into one of the following styles:
- "Generic Humanoid" Hair: Almost always included a recessed hairline to show off the rubber forehead, which on female characters meant to be attractive is usually only slightly bumpy. Also almost always assumes that Aliens Have No Eyebrows, as is frequently the case in Star Trek and in Babylon 5. If this type of alien does have eyebrows, they will be unusually shaped (probably swept-up Romulan-style). The hair can be and frequently is any color.
- "Klingon" Hair- varies from long and thinning (Malons from Voyager) to long, full and luxuriant (Worf, Green Skinned Space Babes from TOS) to long, full and mangy or unkempt (Martok, other Klingons, Nausicaans, Kazon). Again, the hairline is recessed to show off the craggy forehead ridges. Almost always brown or black hair. May or may not come with eyebrows and/or facial hair.
- "Romulan/Vulcan" Hair- typical of Space Nazis and Space Communists. Varies from the near-human looking hair of Vulcans to the super-sleek-and-shiny wigs of Next Generation-era Romulans. Often comes in a bowl cut, or slicked back. Cardassian hair is an example of this. Almost always black hair. Rarely comes with facial hair, unless it is a goatee. Usually look like wigs, and often are. Ditto Aliens love this style.
- "Wookiee" Hair- covers the entire body. Usually a rubber suit alien, but more increasingly represented by Muppets or Serkis Folk. Can be expensive to pull off well. Usually varying shades of brown.
- "Tenctonese" Hair- bald... at least on the head. Usually accomplished by a shave or a bald cap (for example, Babylon 5's female Centauri), often with a pigment pattern or odd texture, and frequently (but not always) are complimented by enlarged craniums suggesting superior intelligence. Again, this is an alien hairstyle that does not often come with eyebrows. Grey Aliens, Martians from Mars Attacks!!, Tenctonese from Alien Nation. The Minbari in Babylon 5 have this is well as "Tenctonese" hairstyles: they are bald with a bony crest that the females have carved and shaped. Although, some Minbari have beards —the ones descended from Valen/Sinclair, maybe? —and obviously, Delenn grew hair after her transformation. Dr. Lazarus on Galaxy Quest's Show Within a Show had a ridged scalp, but was otherwise shorn.
- Not-hair-at-all hair: If the writer (and the budget) allow for aliens who don't have hair but have something else on their heads that they wear like hair. Feathers, scales, or even flowers or vines for Plant Aliens can make for a creative physical difference.
- "Predator" Hair: not actually hair, but bundles of head tentacles/antennae that look like dreadlocks. Usually placed on the head in the same pattern as the Klingons, back from the forehead. Most famously used on the title species of the Predator franchise. Some writers have gone so far as to posit unique sensory organs or symbiotic species. An alien who otherwise looks nothing like Cthulhu might have tentacles, like the unnamed green-skinned Mulder and Scully analogs from the B5 spinoff Crusade, or Ka D'Argo from Farscape. Quarren from Star Wars don't count because they are generic "squidheads." The Protoss of Starcraft naturally have a long bundle of cable-like nerve cords growing out of their head like a ponytail; Dark Templar crop theirs to sever their connection to their race. The Na'vi have tendrils growing out of their head, but in a twist they have hair growing on top of all this over the neural cables. Decapodians from Futurama have bald heads, but tentacle mustaches.
- Genasi from D&D 4th edition have crystals (Windsoul, Stormsoul) or fire (Firesoul) in place of hair, other are simply bald (Earthsoul,Watersoul)