Filling Your Own Hypochlorous Acid Bottles: Why Packaging Must Be Metal-Free
If you buy our Hypochlorous Acid Facial Spray in bulk (1 L to 20 L) to fill into your own bottles, or you send us your own packaging to fill, the packaging you choose matters as much as the formula. Hypochlorous acid (HOCl) is a reactive molecule. In the wrong bottle, or behind the wrong pump, it can lose strength, discolour or damage the sprayer long before its shelf life is up.
The short version: every part that touches the liquid must be metal-free, and the bottle should ideally be opaque HDPE plastic. Here's why, and how to check.
Why packaging matters so much with HOCl
Our spray is around 150 ppm hypochlorous acid in purified water with sodium chloride, buffered to pH 5. HOCl is an oxidant, so it reacts with what it touches. In the right packaging there is nothing for it to react with. In the wrong packaging, three things work against it:
- Metal. Metal corrodes on contact with HOCl and the salt in the formula. That uses up the hypochlorous acid, so the spray loses strength, and it can leave metal residue and discolouration in the product.
- Light. HOCl is light-sensitive. Sunlight through a clear bottle speeds up its breakdown.
- Heat and contamination. Warm storage, and residue from whatever a bottle held before, both shorten its life.
Rule 1: Metal-free, including the parts you can't see
Most people check the bottle and forget the pump. The most common problem is a stainless steel spring inside a fine-mist pump or trigger sprayer, sitting in the liquid. Stainless steel is not safe with HOCl: the salt and the oxidant together attack it.
Check every part that touches the liquid:
- Pump and trigger springs. Choose a plastic spring, or a pump whose spring sits outside the liquid path.
- Valve balls inside pumps and triggers.
- Bottles and caps. No aluminium or metal bottles, and no metal or metal-lined caps.
- Anything you use while filling: funnels, jugs, taps and transfer pumps.
Ask your packaging supplier for the material list or technical drawing for each component, and confirm that no part in contact with the product contains metal. Look for pumps sold as "metal-free" or "all-plastic". If the supplier can't confirm it, don't use it for HOCl.
Rule 2: HDPE plastic, ideally opaque white
High-density polyethylene (HDPE) is our first choice for hypochlorous acid. It resists dilute HOCl and salt, it doesn't corrode, and an opaque white HDPE bottle keeps light out as well. Polypropylene (PP) and polyethylene (PE) are the right materials for the pump, cap and dip tube.
This is exactly what we fill into: a 125 mL opaque white HDPE bottle with a fine-mist pump made entirely of PP and PE, spring included. Our stability testing was done in this packaging, over 12 months at 25 °C and 3 months at 40 °C. The active level stayed within specification throughout, and the packaging showed no corrosion, deformation, leakage or discolouration.
Other materials can work, but we haven't tested them with our HOCl:
- PET and other clear plastics let light in. If you use them, choose an opaque or tinted bottle and keep it out of the sun.
- Glass doesn't react with HOCl, but clear glass lets light in. Choose amber or opaque glass, and the pump or cap still has to be metal-free.
Quick guide
| Part | Choose | Avoid |
|---|---|---|
| Bottle | Opaque white HDPE | Aluminium or other metal; clear bottles kept in the light |
| Pump or trigger | All-plastic (PP/PE) with a plastic spring, or a spring outside the liquid path | Stainless steel springs or valve balls in the liquid |
| Cap | PP or PE | Metal or metal-lined caps |
| Filling equipment | Clean plastic or glass jugs and funnels | Metal funnels, ladles and taps |
Good filling practice
- Use new, clean, dry bottles. Don't reuse bottles that held another product, and never top up a part-used bottle with fresh product.
- Fill in a clean area, recap the bulk container straight away and keep it closed between fills.
- Store the bulk container and filled units below 25 °C, away from direct sunlight and heat.
- Label every unit you fill with the original batch code.
- Open bulk containers within 12 months of your order date. Once a container is open, fill and sell all units within 6 months, and your customers should use them within 6 months of opening.
Sending us your own packaging to fill
Our filling service can fill hypochlorous acid into packaging you supply, but we check it first. Before we fill, we'll ask what each component is made of and confirm that nothing in contact with the product contains metal. Packaging with metal in the liquid path, such as a pump with a stainless steel spring, can't be filled with HOCl. The simplest option is our own 125 mL HDPE bottle and metal-free pump, available as a variant of the Hypochlorous Acid Facial Spray.
Shelf life depends on the packaging
The shelf life and stability data for our Hypochlorous Acid Facial Spray apply to product in our packaging, stored as directed. Once you transfer it into packaging of your choice, checking that packaging is compatible is your responsibility. We can't guarantee the strength, appearance or shelf life of HOCl filled into packaging we haven't tested, and product that has been in contact with metal may lose strength, discolour or damage the pump.
New to HOCl? Read Hypochlorous Acid Spray: The Science Behind Skincare's Gentlest Multitasker.
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This article is general guidance on packaging and storage for our cosmetic hypochlorous acid spray.
