How to stop circular humidity marks in kitchen?

The areas where it is coming from, I would suggest to sand back them areas, filler 1 coat with a light sand when full dry, then one more smooth filler coat and then sand down to smooth the areas filled, apply a watered down light coat with a smooth lay of with the roller, then apply coats with the appropriate kitchen paint needed.

Use mold shield and then kitchen paint.

Open your windows when cooking to avoid a build up of humidity in the air.

You should Keep surfaces dry, Wipe down surfaces frequently to remove any moisture that has accumulated. Install a ventilation fan, consider installing a ventilation fan in your kitchen to remove moisture and improve air circulation.
and use water-resistant paint; If your kitchen walls are frequently exposed to moisture, consider using water-resistant paint that will help prevent the formation of circular humidity marks.

You can get plasterers tape that would solve this problem with.

Disposable and/or compact renewable dehumidifiers can be used in these areas to combat moisture. Eva-Dry dehumidifiers use odorless, non-toxic components to free your kitchen from excessive moisture. You can also use them anywhere in and around your kitchen, cabinets, and pantry

To deal with any residual moisture, consider putting silica gel or camphor in your cabinet. You can buy small packs of it—similar to the ones you find in a new shoe box—from packing supplies stores. These little packs contain crystals that absorb moisture

you have to clean it with a sponge with water, then you will buy a cover stain, paint the stains for a day, let it dry, and then paint it with plastic paint

Sounds like the plaster has been laid on thin or a watered down paint has been used it's very rare if kitchen paint is used that this will happen

The circular marks and lines you're seeing on the kitchen walls could be due to a few different factors related to the plastering and painting process. Here are some potential causes and solutions:

Inadequate Priming: If the walls were not adequately primed before painting, it can lead to uneven paint absorption and result in visible imperfections like circular marks and joint lines. To fix this issue, you can:

Sand the affected areas lightly to create a smooth surface.
Apply a high-quality primer that is suitable for the type of paint you're using (e.g., latex or oil-based primer).
Repaint the walls with the desired paint color after the primer has dried.
Inconsistent Surface Texture: Uneven surface texture on the walls, such as differences in smoothness between the plasterboard joints and the rest of the wall, can cause variations in paint appearance. To address this:

Sand the entire wall to create a uniform surface texture.
Apply a primer and let it dry.
Repaint the walls with your chosen paint.
Insufficient Coats of Paint: Sometimes, applying too few coats of paint can result in the underlying imperfections showing through. If you applied only one coat of paint, consider adding an additional coat or two for better coverage.

Humidity and Condensation: High humidity in a kitchen can cause paint to react differently, leading to visible marks and lines. Cooking and steam can contribute to this issue. While proper ventilation in the kitchen can help reduce humidity levels, you might still see some effects during high-humidity conditions. To minimize this:

Use exhaust fans or range hoods to help reduce moisture in the air during cooking.
Consider using paint specifically designed for high-moisture areas, such as kitchens and bathrooms.
Drywall and Taping Quality: If the drywall installation and taping of the seams were not done properly, it could lead to visible lines and imperfections. Fixing this would require addressing the drywall seams, which might involve re-taping, mudding, and sanding, followed by priming and repainting.

In summary, the issue you're experiencing with circular marks and lines on your kitchen walls could be due to a combination of factors, including priming, surface texture, paint coats, and humidity. To address it, you may need to sand, prime, and repaint the affected areas, ensuring that you create a smooth and uniform surface before repainting. Additionally, consider using paint designed for high-moisture areas to help prevent further issues in a kitchen environment. If the problem persists, consulting with a professional painter or contractor might be necessary to assess and address any underlying issues with the wall surfaces.

Nothing to do with the plaster or the paint. You need to install ether a extractor fan in your kitchen wall or buy extractor hood for above your cooker. If i was you I would install both.

Wherever there are nails just remove the skim and fill it again, then sand it and re coat it. And Wherever you see the joints you can fill it, sand it and re coat it.

Damp stop or cover stain then when dry paint over with Matt emulsion or open a window

Using normal emulsion in kitchens normally show those signs using the right paint for kitchens will not let the moisture into the walls

Not enough plaster re skim wall

Circular humidity marks in the kitchen can be caused by a variety of factors, including insufficient sealing of the walls, poor ventilation, or underlying moisture issues. Here are some steps you can take to address and prevent this problem:

1. **Improve Ventilation:** Ensure that your kitchen has adequate ventilation to help reduce humidity levels. Use exhaust fans while cooking and consider installing a dehumidifier if necessary.

2. **Seal the Walls:** If the walls were not properly sealed before painting, moisture can penetrate through the paint and cause marks to appear. Consider applying a moisture-resistant primer or sealer to the walls before painting to create a barrier against humidity.

3. **Check for Leaks:** Inspect the kitchen for any signs of leaks or moisture infiltration, particularly around plumbing fixtures, windows, and doors. Repair any leaks promptly to prevent further damage to the walls.

4. **Apply Additional Coats of Paint:** If the current paint job is insufficient to withstand high humidity levels, consider applying additional coats of paint or using a paint specifically designed for high-moisture areas such as kitchens and bathrooms.

5. **Address Plastering Issues:** If the circular marks are appearing at the locations of nails or screws used to secure the boards, it could indicate that the plastering or drywall installation was not done properly. You may need to consult with a professional to evaluate the condition of the walls and determine if additional coats of plaster or repairs are necessary.

6. **Use Mold-Resistant Paint:** Consider using a mold-resistant paint for the walls in the kitchen, especially in areas prone to high humidity. These paints contain additives that inhibit the growth of mold and mildew, helping to prevent moisture-related issues.

7. **Monitor Humidity Levels:** Keep an eye on the humidity levels in your kitchen using a hygrometer. Ideally, indoor humidity levels should be between 30% and 50%. If humidity levels consistently exceed this range, you may need to take further steps to address ventilation or moisture issues.

By addressing these factors and taking proactive measures to prevent moisture buildup in your kitchen, you can help reduce the occurrence of circular humidity marks on the walls. If the problem persists despite your efforts, consider consulting with a professional contractor or painter for additional assistance.

You may need an extractor fan installed.
For your existing wall issue,you can use a block stain paint which will prevent moisture returning and will whiten the area affected.Once dry,you will need to repaint that area/wall with the desired colour.