Skin

A skin is a graphic file in The Sims,The Sims 2, and The Sims 3 which are used to represent the head, body and clothing of a Sim, but how they work in the three games is somewhat different. The wide availability of third-party skins has unquestionably contributed to the high visibility of the series.

And let me guess, I won't be able to download peploes houses or sims if they've used the furniture I'll need to pay hundreds of dollars to get all of? Why do people even need this? what did you do to The Sims, EA? Make it so people can't add their own custom furniture and clothing and everything they loved to make for free in Sims2? Players happily created things for free so clearly this wasn't necessary. I'll wait until the game comes out so I can see reviews but I swear, if you removed custom content, I will pirate every last bit of Sims 3 and probably every game you ever make from now on. You already jipped me off when I bought your 3D object putter-togetherer you named spore  that you advertised as an evolution simulator and I'm not going to let you do it again. And EA I assure you, I am not alone. And let me guess, I won't be able to download peploes houses or sims if they've used the furniture I'll need to pay hundreds of dollars to get all of? Why do people even need this? what did you do to The Sims, EA? Make it so people can't add their own custom furniture and clothing and everything they loved to make for free in Sims2? Players happily created things for free so clearly this wasn't necessary. I'll wait until the game comes out so I can see reviews but I swear, if you removed custom content, I will pirate every last bit of Sims 3 and probably every game you ever make from now on. You already jipped me off when I bought your 3D object putter-togetherer you named spore  that you advertised as an evolution simulator and I'm not going to let you do it again. And EA I assure you, I am not alone.

The Sims 2
With the advent of the full 3d environment in The Sims 2 (See Comparison between The Sims and The Sims 2), skins become more complex. Skins are still in BMP format but are now contained in a "package" file, which can be extracted (and compiled) with the included Body Shop tool.

A Sim's body is now separate from their clothing, and there are now 4 basic skin tones (light, medium-light, medium-dark and dark) with each skin tone's graphic files being divided by age and gender. In addition, custom skin tones are now possible, and many are available as custom content. That Sims' bodies and clothing are separate makes all outfits available to all Sims of the appropriate age and gender, regardless of their skin tone or body shape. It also means it is now possible to create distinguishing marks such as tattoos that are unique to a Sim, although in practice this is not an economical use of drive space.

Hair is also separate, with different colours and styles, and eye colour can also be set. These traits are carried in a Sim's genetics, and passed on to their children. While The Sims 2 generally distinguishes between custom skins and those included with the game, hair is a partial exception. Some hair creators place their creations in their appropriate color bins. Hair that has been "binned" will still be marked as custom content, but it will not be treated as custom hair, and the game may use it when assigning hair to a newly generated Sim.

Sims can change their appearance through a mirror. Hair colour, hairstyle, facial hair (male teens and older only) make-up, glasses/head accessories, and face paint can be changed.

Clothing has also undergone changes. Not only is there far more detail, but when wearing their Everyday clothes the top half of a Sim's outfit can be made separate from the bottom half, or simply be one piece. The modes of dressing are Everyday, PJs, Underwear, Swimwear, Formal, and Gym Clothes/Workout Gear. Seasons added Outerwear, which will usually be worn in cold weather. Unlike The Sims, which used file-naming conventions to identify skins as Everyday, Formal, etc., The Sims 2 uses internal flags. While separate tops and bottoms can only be Everyday, whole outfits can placed in multiple categories. For example, an outfit can be flagged as both Everyday and Gym Clothes.

The Sims 2 also uses internal flags to show which life stages can wear an article of clothing, and which gender it is for. SimPE can be used to set these flags, but it is not recommended to have an article of clothing available to more than one life stage unless the stages are young adult and adult. Likewise, an article of clothing can be flagged as being for both genders. This can be, and sometimes is, done with clothing for toddlers and children, as their bodies do not have gender differences. However, it is not recommended to have clothing for older Sims flagged as being for both genders.

Pregnant Sims will wear maternity clothes, although this can't be assigned by players. However, there is at least one mod which allows players to use custom outfits as maternity wear, provided that those outfits were created with that in mind.

The Sims 3
In The Sims 3, players can choose from one of the 6 base colors offered and then use the sliders for a more customized skin tone. Custom skins are also available. The base game doesn't include life stages such as aliens and vampires, but it is possible to create Sims which resemble them by using pale green tones and pale blue tones.