How to Make Cold Process Soap with Lye

While we’ve tried a few different soap-making methods here on Hello Glow, there’s still one method that we haven’t yet tackled: soap with lye.

I consider myself a pretty fearless DIYer (I mean, what could possibly go wrong with a half-pound of charcoal and some citric acid?) but I have always been a little nervous when it comes to making soap the old-fashioned way. Especially when I can just purchase melt-and-pour soap and be done with it. But after getting into a bad of batch of the melt-and-pour stuff recently, I decided it was time to overcome my fears and learn how to make my own soap from scratch.

With a little research I found that there’s a reason people still make soap the old-fashioned way. Back in the day, lye soap was used to clean everything from clothes and stains to dishes and floors. It was even kept in the medicine cabinet to treat poison ivy, soothe rashes and take the itch out of bug bites.

The secret? A high lye content combined with pure animal fat (i.e., no fancy oils) gives traditional soap extra cleaning power while still retaining moisture and healthy fats.

Since I like soap to be a tad on the softer side, I made mine with less lye and a higher fat content. Then I scented it with lemon essential oil and a touch of bergamot for aromatherapy purposes.

I also added some poppy seeds for contrast and light exfoliation. Not only will this lemon poppy seed soap leave your skin feeling fresh and clean, but it can also be used as a household cleaner in a pinch.

Cold process lemon poppy seed soap

How to Make Cold Process Soap with Lye

There are a lot of different lye soap recipes floating around the internet, and sometimes it can seem a little overwhelming. While you don’t need a lot of ingredients to make your own soap, you do need to take extra precautions when working with lye. Here a few things to keep in mind before you get started:

1. When mixed with water, lye creates toxic fumes and can burn your skin. Always wear gloves, long sleeves and goggles to prevent burns should you accidentally spill or splash it on yourself. Mix lye with water in a well-vented area (outside is even better) and keep white vinegar nearby in case you do happen to splash some on yourself.

2. Always add lye to water, never water to lye. Adding water to lye can cause an eruption that can burn you!

3. Use old supplies for making your soap and keep these separate from your everyday cooking supplies. Once something has touched lye, you really don’t want it to come in contact with food.

4. When it comes to molds, you can use an old loaf pan lined with wax paper or you can purchase silicone soap molds. I used a pre-formed bar soap mold because it came free with the lye I purchased from Amazon (huzzah!), but you don’t need a fancy soap mold. An old loaf pan will do fine, and you can slice the soap once it’s hardened.

5. Use a lye calculator to figure out exactly how much lye and water you need for your particular type of fat. Then pre-measure your ingredients and have them at arm’s length so you can work quickly once your start mixing things together.

How to make cold process soap with lye


  • 16 ounce glass jar
  • Small glass or plastic dish (for holding dry lye flakes)
  • Stainless steel pot (lye reacts with aluminum creating toxic fumes)
  • Immersion blender
  • Kitchen scale
  • Soap mold
  • Candy thermometer
  • Gloves, goggles and a face mask

Soap Ingredients

Once you’ve gotten all your supplies together, watch this quick video (and read the detailed instructions below!) showing you how to make cold process soap.

Cold Process Soap Instructions

1. If you’re using a glass or wooden mold, line it with wax paper.

2. Put on your protective gear. Place your glass jar on the kitchen scale and tare your scale. Pour filtered water into the jar until it reads 10.5 ounces. Then set aside.

3. Put the small glass or plastic dish on the scale and tare the scale again. Carefully pour lye into the dish until it reads 4.25 ounces. Note: static electricity can cause the lye to cling to your gloves or clothing. If this happens, carefully brush it off outside and use white vinegar to neutralize it if you get any on your skin.

4. Go outside and slowly pour the lye into the water. Stir the mixture until the lye is completely dissolved. As you stir, the mixture will become quite hot so be careful if you need to move it. Let it cool to between 100-120 degrees.

5. Meanwhile, place the lard in a stainless steel pot and put it on the burner. Heat over medium heat until completely melted. Remove the oils from the heat and let cool to between 100-120 degrees. Use a candy thermometer to test the temperature every 5-10 minutes until it reaches the desired temperature. If one is cooling faster than the other, put your oils back on the burner or place the lye/water mixture in a warm water bath to slow the cooling. Ideally you want the lye/water and the oils to both be between 100-120 degrees and within 10 degrees of each other.

6. Slowly pour the lye/water into the oils. Place your immersion blender in the pot, making sure the blade is completely submerged in the mixture, and blend until the soap mixture resembles cake batter (about 3-5 minutes).

7. Add the turmeric, poppy seeds and essential oils.

8. Pulse the immersion blender a few more times to incorporate the add-ins. Lift the blender up and see if the drips leave a trail or “trace” on the surface of the soap mixture (this is called “medium trace”). If so, pour the soap into your mold. Remember that the soap is not fully “cooked” yet at this point and could still irritate your skin so you should still be wearing your gear.

9. Put the mold somewhere warm (like an oven with the light on) and let it sit for 24 hours.

10. After 24 hours, pop your soap out of the mold and cut if needed. Stand bars up in a dry area with space in between each one to allow for air circulation. Let them sit for 4-6 weeks to let the soap finish hardening. The soap will lose some of its water during this time making the bar harder and longer lasting.

11. When you’re done (with your gloves still on) rinse any supplies that had lye or soap mixture in them with running water. Pour some vinegar in a sink filled with hot soapy water and wash everything in there, then set aside away from your food prep area to dry. Store all soap making tools in a closet or cabinet away from food.

Lemon Poppyseed Cold Process Soap

More Cold Process Soap Recipes

If you feel like you’re getting the hang of it, here are more cold process soap recipes you could try: 

DIY Olive Oil Soap

Even if you’re not usually a fan of bar soap, this DIY olive oil soap will have you singing a different tune – it’s gentle, creamy, and it can be used on anything from moisturizing your skin to treating laundry stains. 

Honey + Turmeric Soap

This all-natural, head-to-toe beauty bar is infused with turmeric, raw honey, and witch hazel, and clears acne, leaving your skin bright and clear. It contains additional plant butters and oils to help hydrate as it cleanses, which works wonders on the skin. 

How to make a shampoo bar recipe

Cold Process Shampoo Bar

Shampoo bars are all the rage right now (thanks to the recent waste awareness!) and there’s no reason you shouldn’t make your own. This cold process recipe is made for fine and oily hair, hydrating it without weighing it down. 

Homemade Laundry Soap with Lavender and Lemon

Lavender and Lemon Herbal Laundry Bar Soap

Green up your laundry routine with a cold process lavender and lemon herbal soap bar. The experience of taking your fresh clothes out of the wash with the lovely scent from your handmade laundry bar is not only valuable and satisfying, but your skin will also surely thank you for choosing all-natural ingredients that boost skin health


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