Though it's more common to hear them referred to as custom content if they don't actually modify the way that the game functions, mods have been a key part of every generation of The Sims series, including The Sims 3. There are custom versions of clothes, make-up, accessories, and pretty much anything that your heart could ever desire!
There's so much variety out there that it's almost impossible to narrow it down, but this list covers the basics. If you want to change your Sims 4 experience but only from a visual standpoint, you definitely need to give these impressive mods a try!
10 Default Replacement Eyes
According to William Shakespeare himself, "The Eyes are the window to your soul." That quote still holds true for Sims, apparently, since default replacement eyes have been around since The Sims 2. They completely change the aesthetic of a Sim with just a simple file addition to the mods folder.
In The Sims 4, there are a handful of occult types in addition to regular Sims, and three of them have their own eyes: Vampires, Mermaids, and Aliens. It's important to some simmers to use default replacements from the same set so they look uniform across all different types of Sims, but unfortunately, it's not really common to find a complete collection.
Luckily, MissRubyBird has made a complete set that's absolutely beautiful called Aqua Trigger Eyes. In addition to the 18 default colors, there are several natural and unnatural colors, as well as central heterochromia and even pets. The designs for the Vampire, Mermaid, and Alien eyes are all inspired by EA's actual textures, so they're seamlessly Maxis match!
9 Eye Shine Removers
The Sims 4 has a specular map in the eyes which causes light to reflect in them. It's a really great idea, but some people find it a bit jarring when it comes to the purely aesthetic part of the game. Luckily, there are a couple of dedicated simmers out there who came up with a solution.
LumiaLoverSims has an eyeshine remover that makes them totally matte by default, with different mod flavors allowing you to choose whether you want to apply it to all occults or just some of them. If matte isn't really your cup of tea, Alf-Si has a set of bright reflections that can be applied as make-up to give your Sims' eyes a splash of light!
8 Default Replacement Skins
Default replacement skins are probably one of the most basic mods for The Sims series overall. They first showed up during The Sims 2 era and they've been prevalent ever since. Some completely overhaul EA's texture and turn it into something of its own, while others linger more closely to the original aesthetic of the game.
LumiaLoverSims has two different default skins. Vanilla is an upgraded version of the default EA skin for all ages that comes with several additional details like belly and chest overlays. Smoothish II is only available for teens - elders, and it ventures further out from EA's default skin with well-defined body textures and smoothly sculpted facial features.
7 Skin Details
There are several "slots" on each Sim's face that can be used to add a lot of minor details, from freckles and moles to different types of wrinkles and even acne. Lots of simmers use the skin details section to implement their custom content.
One of the most useful skin details is Pyxis' famous About Face, a facekit that consists of a ton of small details including highlights and shadows. It shows up in several categories so the details can easily be layered to give each Sim a unique appearance.
6 3D Eyelashes
EA's eyelashes are simply a block of black with no real detail to them, which isn't objectively a bad thing, but there's nothing wrong with wanting to upgrade from what was shipped out with the base game. 3D eyelashes are one of the most simple pieces of custom content, and yet they can truly make or break a Sim's appearance!
Kijiko has several different types of 3D eyelashes available - and yes, they are the ones that you've been seeing everywhere on the internet. There are long, dramatic ones and short, simple ones, as well as uncurled ones that give a naturally relaxed look. They're available for all ages, from toddler - elder, and they can be used as a skin detail (so they stick to every outfit, no matter what,) or an accessory (which has to be reapplied every time you switch outfits,) depending on personal preference!
5 Custom Teeth
Different types of teeth were added in a free update in January 2017, including some nice touches like braces and imperfections. When The Sims 4: Vampires was released, it added several different fangs and The Sims 4: Get Famous even came with some new options, but the community has a plethora of custom versions available as well.
Magic-bot has a set of default replacements that make teeth shinier, more pronounced, and a lot more realistic. They can also be downloaded in a non-default version, in case you're just looking to expand on your options, rather than replace them altogether. Pyxis has a texture replacement mod that simply replaces the textures with more defined, neat, and overall aesthetically pleasing ones. There are also several other teeth-related mods available from Pyxis!
4 Body Mods
The default body shape from The Sims 4 isn't bad at all, but some simmers who are into slightly more realistic things will probably appreciate the knowledge that there are replacements out there.
LumiaLoverSims released a set of upper body replacements for teen-elder Sims in his Body Redux 3 set. For male frames, there are two different versions available: the lean one which can be used as a default replacement, and the muscular one that functions as a top for swimsuits, sleepwear, etc. Each one adds a more defined, realistic body shape. For female frames, there are three different choices that practically do the same thing: a softer, more supple figure.
Both versions add more detail to the chest and get rid of the Barbie-like aspect of the default body shape!
3 HD Feet
The Sims 4 suffers from an unattractive phenomenon known as block feet. No matter how beautifully detailed a Sim's skin might be, it will pretty much always be thrown off by the fact that their feet are... well, blocks. It's not really a good look in screenshots or in gameplay in general, but luckily, Necrodog has stepped up to the place with a mod called HD Feet.
Available for all ages, it does pretty much exactly what it says. It gives definition to sims of all ages' feet and the most recent release (V6) comes with a set of overlays to add even more detail. It's also recommended to grab SimmingLena's Wearable Maxis Feet, since the HD Feet mod makes all socks into toe socks.
2 Custom Sliders
The ability to simply grab a Sim's face and change it at will is one of the most appealing parts of The Sims 4. However, after a while of playing around with the same facial features, it can become a little stale. Of course, that's not really an issue when the community is more than ready to take care of that problem.
TeanMoon has made a couple of different sliders that expand the scale for the mouth and nose. Obscurus-Sims has made several sets of sliders for the face, including the eyes, eyebrows, mouth, and nose. There are a ton of other sliders out there as well, including several body sliders from cmar.
1 Hair Recolors
There are a total of 18 hair colors in The Sims 4. There are 9 natural colors which are available to all ages that range from black to blonde, while the others are only for teens and up. There are 4 unnatural hair colors, 2 graying natural colors, and 1 shade each of white and gray for elders (or experimental youths.)
Obviously, it can get repetitive being stuck with the same few choices, but again, custom content saves the day! There are a lot of different palettes out there, but there are few more popular than WildlyMiniatureSandwich's range of 55 shades, which includes 35 unnaturals, 20 naturals, and 20 neutrals. She has recolored several EA hairs in her own palette, and made the resources publicly available for anyone else to use them to make recolors, too.