You did two popular mistakes here.
- you sculpted the lips on the head and not from it.
- you forgot the facial muscles that are all around the mouth.
These are the reasons why your lips look so "attached" to the head and not integrated. Also, the philtrum (purple area) looks a bit too big and dominant. And, your model has no chin (green area), and there is no nose. These missing parts can make it look strange.
If you're new to sculpting
- start with a whole head. Even if you want to focus on the mouth add a basic nose, chin, cheeks, eyes, and ears. These are helpful landmarks for orientation and to get the proportions and locations right.
- start low-poly, add geometry when you need it (use the voxel remesher or Dyntopo to increase the resolution)
- use a focal length of
85 or higher for the viewport. The default value is 50 and it shows a lot of perspective/lens distortion if you zoom close to your model. Classic headshot portrait photos often have a focal length of 80 or more.
- use reference images and make sure the focal length roughly matches the reference
- don't be frustrated. Sculpting for likeness is very difficult. Take breaks to refresh your eyes and spot mistakes you didn't notice before. If you work too long with the model, you will become blind to mistakes.
from How Focal Length Can Dramatically Change Portraits
How to Sculpt the Mouth
One technique to sculpt a mouth is to dig the mouth corners, then crease in the center line of the lips. Pull out the lips a little and add clay around the mouth where the muscles are, smooth everything around the mouth corners.
Lips come in all shapes and sizes and their appearance can vary a lot. But all lips have muscles and fat around them. They can be visible more or less. Also, wrinkles can be visible more or less.
How to Fix Your Model's Lips
TL;DR → 10 Most common head sculpting mistakes that even experienced artists make
You have already nicely modeled lips so you can fix them just by adding some clay around the mouth and the chin. Try the Clay Strips and the Clay brush. Later is a bit softer.
- image top left:
- I remodeled the lips as best I could and marked the problem areas
- image top right:
- fill up the areas around the mouth, and just a little for the philtrum
- make a little "hill" for the chin.
- dig two little holes in the mouth corners with the Draw Sharp brush. Then add more clay to the upper lip (left and right) and a bunch of clay right next to the mouth corners. There is a muscle. You can see it on the girl above, the left image. Have a look at the shadow and the highlights right next to the mouth corners.
image bottom left:
- smooth everything.
- make sure that the transition of lip and skin on the left and right of the bottom lip is soft and that it flattens very easily (blue areas, bottom). Look at the shadow. The shadow is only visible right below the bottom lips, not left and right.
- below the center of the bottom lip, there are fewer muscles and fat. There is a steeper flattening. The transition between lip & skin is more visible.
- if you want you can make the width of the lower lip slightly narrower.
image bottom right:
- if you carefully smooth the top lip above the mouth corner and the sides of the bottom lip you will automatically get a nice mouth corner with a crease/wrinkle. The creases/wrinkles go from the mouth corners down. But sometimes they can go up a bit into the top lip (see reference image above). Young people have it less visible and it's smaller but the wrinkles grow with age.
- polish (smooth) everything, and make the philtrum a bit smaller (Elastic Deform brush)
- if you want a more realistic appearance then flatten/soften the edges of the upper lip a bit. If you keep it "sharp"/prominent it will look more stylized.
Make sure that the upper lip skin does not fall too much into the face. Otherwise, the nose is pushed too much into the face and you have a "French Bulldog Human". The slope between the edge of the lip and the nose is rather steep.
The upper lip itself is usually rather flat and slanted inward, while the lower lip is often curved. Of course, this depends on the size, fullness, and shape of the lips.
A Few More Examples
- is the example from above with a slightly reduced width
- tries to keep the shape of your modeled lips as much as possible
- small lips, weakly pronounced bottom wrinkles at the corners of the mouth, wrinkles go into the top lip
- soften the edges of the lips, looks more natural and less stylized
- the lower lip is not as wide as the upper lip, and the skin of the face is visible on the left and right sides of the lower lip. (the chin needs more love)
- very subtile mouth corners (used a photo as reference)