Most people asking about silica mean the small sachets marked “silica gel — do not eat” that come packed with shoes, electronics and vitamins. They are a drying agent, they are there to stop moisture damaging the product, and they are far less dangerous than the warning suggests. Silica also appears in medicine, as magnesium trisilicate in antacids.
What is Silica?
Silica is silicon dioxide — one of the most abundant compounds on earth. Sand, quartz and glass are all largely silica.
Silica gel, the sachet kind, is not a gel in any everyday sense. It is a hard, porous granular form of silica with an enormous internal surface area — a single gram has a surface area of several hundred square metres, riddled with microscopic pores. Those pores hold water molecules by adsorption, pulling humidity out of the air in a sealed package.
It can absorb roughly a third of its own weight in water, which is why one small sachet protects a whole shoebox.
The “do not eat” warning is standard labelling, not a poison warning. Silica gel is chemically inert and essentially non-toxic — it passes through unchanged. If a child swallows a sachet, it is very unlikely to cause harm. The real risks are choking on the sachet itself, and the old blue or orange indicator beads, which were coloured with cobalt chloride — a genuine toxin, now largely phased out. Still contact a doctor or poison centre if a child has swallowed one, particularly a coloured one, and take the packet with you.
Where silica meets medicine: the South African Medicine Price Registry lists Bisma-Rex Powder, a Schedule 2 antacid containing magnesium trisilicate with aluminium hydroxide and calcium carbonate. Magnesium trisilicate is a silicate salt used to neutralise stomach acid, and it is a genuine registered medicine ingredient. Silica gel sachets are not medicine and are not related to it.
Silica also appears as colloidal silicon dioxide, an inert flow agent in tablet manufacture, and as silicon supplements for hair, skin and nails — where the evidence is thin.
What is Silica commonly used for?
Silica gel sachets — the everyday uses:
- Keeping packaged goods dry — shoes, leather, electronics, cameras, vitamins, supplements and food.
- Protecting tools and metal items from rust in a toolbox or safe.
- Drying documents, passports and photographs in a humid climate.
- Protecting stored seeds from mould, and keeping camera optics free of condensation.
- Drying out a wet phone — this works, but far less well than claimed, and rice works worse still. A proper drying pouch or a repair shop is better.
- Reducing damp in a safe, jewellery box or storage container, and preserving dried flowers buried in loose beads.
Magnesium trisilicate — the medicine use:
- Neutralising stomach acid for heartburn and indigestion, in antacid powders and tablets. It reacts with acid to form a protective gel, hence the name.
Silicon supplements are marketed for hair, skin, nail and bone health. There is some interest in silicon’s role in connective tissue, but the evidence that supplementing helps is weak, and deficiency is not a recognised problem on a normal diet.
How Silica fits into this medicine category
A note on where this page sits: silica gel is a desiccant, not a medicine, and this page appears in the digestive category because of the silicate antacid connection. This placement is being corrected.
The genuine medical relatives are:
| Group | Examples | What it does |
|---|---|---|
| Silicate antacids | Magnesium trisilicate (Bisma-Rex) | Neutralises acid; forms a protective gel |
| Other antacids | Aluminium hydroxide, calcium carbonate, Gaviscon | Neutralise acid directly |
| Alginates | Gaviscon | Raft over stomach contents |
| H2 blockers | Famotidine, cimetidine | Reduce acid production |
| Proton pump inhibitors | Omeprazole, pantoprazole | Strongest acid suppression |
| Antispasmodics | Hyoscine (Hyospasmol) | Cramping, not acid |
| Anti-nausea | Metoclopramide (Adco-Contromet) | Nausea and stomach emptying |
See the digestive and stomach medicines hub.
What to check before using Silica
For silica gel sachets:
- Keep them away from small children and pets. Not because they are poisonous, but because the sachet is a choking hazard and the beads are attractive to a toddler.
- Check the colour. Plain white or clear beads are inert. Blue or pink indicator beads may contain cobalt chloride, which is toxic and has been phased out in most markets. Orange indicating gel uses a safer dye. If in doubt, treat coloured beads as the ones to be careful with.
- Do not put them in food containers unless the sachet is specifically food-grade.
- They can be dried and reused. Heating the beads in a low oven — around 100 to 120 °C for a couple of hours — drives off the moisture and restores them. Coloured indicator beads return to their dry colour when done.
- They do not last forever in a sealed package; once saturated they stop working.
For magnesium trisilicate antacids, speak to a pharmacist if you:
- Have kidney disease. Magnesium and aluminium accumulate when the kidneys are impaired.
- Take thyroid medicine, iron, bisphosphonates, or antibiotics such as doxycycline or ciprofloxacin. Antacids bind these — separate them by at least two hours.
- Are on a low-sodium diet, since some antacids carry a sodium load.
- Need it regularly for more than a couple of weeks, which needs assessment rather than continued self-treatment.
For silicon supplements, check what form and dose you are taking, and be sceptical of hair-and-nail claims.
Possible cautions and when to ask a pharmacist or doctor
If someone swallows silica gel:
- Adults and older children: almost always harmless. Drink some water. The beads pass through unchanged.
- A small child, or any coloured beads: contact a doctor or a poison information centre, and take the packet with you so the type can be identified.
- Get emergency help if someone is choking, coughing persistently, wheezing, or having difficulty breathing after putting a sachet in their mouth — the sachet itself is the real hazard.
Silica dust is a different matter entirely, and a serious one. Breathing fine crystalline silica dust — from cutting, grinding or drilling concrete, stone, tiles or engineered stone worktops — causes silicosis, an irreversible scarring lung disease, and raises the risk of lung cancer and tuberculosis. This is an occupational hazard, not a sachet hazard, but it is the genuinely dangerous form of silica and it matters in South African mining and construction. Anyone doing that work needs proper dust suppression, extraction and respiratory protection, and should have regular occupational health screening. See a doctor for a persistent cough, breathlessness on exertion, or chest tightness after years of dusty work.
For antacid use, seek advice for:
- Persistent heartburn — most days for more than two weeks.
- Difficulty or pain swallowing, unintentional weight loss, persistent vomiting, vomiting blood, black tarry stools, or anaemia. These need prompt assessment, not an antacid.
- New indigestion over the age of 45 to 50.
- Constipation or diarrhoea from regular antacid use — aluminium constipates, magnesium loosens.
Get emergency help for severe chest pain, particularly with breathlessness, sweating, nausea, or pain spreading to the arm, neck or jaw. Reflux and cardiac pain feel similar, and an antacid is not a test.
Related medicine guides
Frequently asked questions
What is silica gel used for? Absorbing moisture. The sachets keep packaged goods dry — shoes, electronics, cameras, vitamins, documents, tools and seeds.
Is silica gel poisonous? No. It is chemically inert and passes through the body unchanged. The “do not eat” label is standard warning text. The real risks are choking on the sachet, and older blue or pink indicator beads which may contain toxic cobalt chloride.
My child ate a silica gel packet. What should I do? Contact a doctor or poison centre and take the packet with you, particularly if the beads were coloured. Get emergency help if there is coughing, wheezing or difficulty breathing.
Can I reuse silica gel? Yes. Heat the beads in a low oven, around 100 to 120 °C for a couple of hours, to drive off the moisture.
Does silica gel dry out a wet phone? Better than rice, but not as well as claimed. A proper drying pouch or a repair shop is a better bet.
Is silica a medicine? Silica gel is not. But magnesium trisilicate, a silicate salt, is a registered antacid ingredient — it appears in products such as Bisma-Rex Powder.
Are silicon supplements worth taking? The evidence for hair, skin and nail benefits is weak, and silicon deficiency is not a recognised problem on a normal diet.
Is silica dust dangerous? Yes, seriously. Fine crystalline silica dust from cutting or grinding stone, concrete or engineered stone causes silicosis, an irreversible lung disease. That is an occupational hazard requiring proper protection — quite separate from the sachets.