Calendula is one of the best botanicals for a sensitive scalp. Its anti-inflammatory, soothing and skin-softening properties make it ideal in a shampoo bar, especially when paired with a gentle, low-cleansing formula. Below is a cold-process shampoo bar recipe designed for sensitive scalps, plus a gentler pH-balanced alternative if your scalp reacts to traditional soap-based bars.

Why calendula works in shampoo bars

Calendula contains flavonoids and triterpenoids that help calm redness, itching and irritation. In shampoo bars, calendula is usually added as an infused oil or glycerin-based extract. For sensitive scalps, it is best to keep the formula simple, avoid aggressive cleansing oils, and skip or heavily limit fragrance.

Cold-process calendula shampoo bar recipe

This recipe makes approximately 500 g of oils, which yields about 5-6 bars depending on your mold. Always run the final formula through a lye calculator and follow safe soap-making practices.

Ingredients

  • 200 g calendula-infused olive oil (40%)
  • 75 g coconut oil (15%)
  • 100 g shea butter (20%)
  • 50 g mango butter (10%)
  • 25 g castor oil (5%)
  • 50 g sweet almond oil (10%)
  • 65.7 g sodium hydroxide - adjusted for 7% superfat
  • 133 g distilled water - for a 33% lye concentration
  • Optional: 1 teaspoon colloidal oatmeal, 1 teaspoon calendula extract

How to make calendula-infused oil

  1. Fill a clean jar about one-quarter full with dried calendula petals.
  2. Pour your chosen liquid oil over the flowers until they are fully covered by at least 2-3 cm of oil.
  3. Seal and infuse in a warm, dark place for 4-6 weeks, shaking gently every few days.
  4. Strain through a fine mesh or cheesecloth. Use the infused oil in the recipe.

If you need the oil faster, heat the oil and dried calendula gently in a double boiler at 50-60°C for 1-2 hours, then strain. Do not use fresh calendula flowers, as their water content can cause spoilage and lye issues.

Step-by-step method

  1. Prepare your workspace. Wear safety goggles, gloves and long sleeves. Work in a ventilated area.
  2. Weigh the oils and butters. Melt the coconut oil, shea butter and mango butter gently until just liquid. Add the calendula-infused olive oil, castor oil and sweet almond oil. Cool to around 38-43°C.
  3. Mix the lye solution. Weigh distilled water and sodium hydroxide separately. Add the lye to the water, never the reverse. Stir until dissolved and allow it to cool to around 38-43°C.
  4. Combine. Slowly pour the lye solution into the oils. Use a stick blender in short bursts, stirring between bursts, until the mixture reaches a thin trace.
  5. Add extras. At trace, stir in colloidal oatmeal and calendula extract if using. Do not add large pieces of dried flowers, as they can become scratchy and encourage mold.
  6. Pour into a mold. Tap the mold gently to release air bubbles. Cover and insulate lightly.
  7. Cut and cure. After 24-48 hours, unmold and cut into bars. Cure in a cool, dry place with good airflow for at least 4-6 weeks. This reduces the soap’s alkalinity and creates a milder bar.

Tips for sensitive scalps

  • Keep the cleansing value low. This recipe uses only 15% coconut oil to produce gentle lather without over-stripping the scalp.
  • Skip fragrance or use very little. Essential oils can be irritating to sensitive scalps. If used, choose skin-safe options like lavender or German chamomile at a low rate, or omit entirely.
  • Use an acidic rinse. Traditional soap-based shampoo bars have an alkaline pH. After shampooing, rinse with diluted apple cider vinegar - about 1 tablespoon vinegar in 1 cup of water - to help smooth the hair cuticle and rebalance the scalp.
  • Patch test first. Try the bar on a small area of skin before using it on your scalp.

Gentler alternative: pH-balanced calendula shampoo bar

If your scalp is extremely sensitive or prone to dermatitis, a syndet shampoo bar is often gentler than lye-based soap because it can be formulated closer to the scalp’s natural pH. To make a simple version, melt a ready-made shampoo bar base, then stir in 1-2% calendula glycerin extract or a small amount of calendula-infused oil. Add 1% dl-panthenol for extra soothing, pour into a mold, and allow it to cool. This gives you the scalp-calming benefits of calendula without the high pH of traditional cold-process soap.

With the right formula and a proper cure, calendula shampoo bars can be wonderfully soothing for sensitive scalps. Start with small test batches, keep the ingredient list simple, and let your scalp tell you what it likes.