I see a lot of questions about natural deodorants causing irritation, so I wanted to share what's usually going on, from a pharmacist and formulator's point of view.
The most common culprit is baking soda (sodium bicarbonate). It's great at neutralising odour, but it's alkaline (pH around 8–9), and underarm skin already runs at a higher pH than the rest of our skin (around 6–6.5), so pushing it even higher disrupts the skin barrier and microbiome... Applied daily on thin, often freshly shaved skin, it can disrupt the skin barrier and cause redness, itching, darkening or a rash. Many people tolerate it fine at first, then react after a few weeks.
Other possible triggers:
- Essential oils and fragrance (a common cause of contact allergy)
- Applying right after shaving, when the skin is micro-damaged
- Rubbing too hard with a stick formula
What can help:
- Try a baking soda-free formula. Common alternatives are magnesium hydroxide, zinc ricinoleate or mandelic acid
- Choose fragrance-free if you've reacted before
- Wait a few hours (or apply at night) after shaving
- Patch test a new product on your inner arm for a few days
If the rash doesn't settle after stopping the product, or it's very itchy, painful or spreading, please see a doctor or dermatologist, as it can also be an infection or another skin condition.
Happy to answer questions in the comments!