Before anything else: check your manual. Some machines want a drop of oil in the hook race every few hours of sewing. Others are sealed and lubricated at the factory, and adding oil actively harms them. There is no universal rule, and applying one to the wrong machine is the most common oiling mistake.
What sewing machine oil actually is
Sewing machine oil is a highly refined, low viscosity white mineral oil. Three properties matter. It is thin enough to reach tight clearances by capillary action. It is clear and non-staining, so a small amount reaching fabric is less likely to mark it permanently. And it is chemically stable, so it does not gum or varnish as it ages the way vegetable-derived oils do.
This is why substitutions fail. Cooking oil oxidises into a sticky film that seizes mechanisms. Multi-purpose penetrating sprays are solvent-heavy, thin existing lubricant, creep into places you do not want them, and can attack plastics and finishes. Motor oil is far too viscous for the clearances involved.
Mineral oil is not hazardous in the way solvents are, but it is not inert either. Chemical hazard data on mineral oil records that inhalation of vapour or mist can cause aspiration pneumonia and lipid pneumonia, that eye irritation is the main direct contact concern, and that skin contact should be limited with protective measures and prompt washing. In practice: use it in a ventilated space, do not decant it into unlabelled containers, keep it away from children, and follow the supplier’s safety data sheet. Any exposure concern is a question for a clinician or a poison information service, not for a maintenance guide.
Machines you must not oil
Many machines built since roughly the 1990s use sealed bearings and self-lubricating bushings made from oil-impregnated sintered materials. Adding oil to these can wash out or dilute the designed lubrication, and excess oil attracts lint, forming an abrasive paste.
Manufacturers signal this in the manual, usually with an explicit statement that the machine requires no lubrication or that lubrication is a service-centre task. If your manual says that, believe it. If you have no manual and cannot identify the model, treat it as a question for a technician rather than guessing.
The hook race, if yours is oilable
Where user oiling is specified, the hook race is usually the only point. It is the circular track the hook rotates within, under the throat plate. It is a high speed sliding contact with a genuine need for lubrication, and it is also the point closest to your fabric, which is why quantity matters so much.
The procedure, where the manual calls for it, is: switch off and unplug, remove needle, foot, throat plate, bobbin and bobbin case, brush out all lint first, then apply one drop to the specified point, and turn the handwheel by hand several times to distribute it. Oiling over lint simply creates lubricated lint.
How much is too much
One drop. Not a squirt, not a bead running along a surface. Excess oil does not improve lubrication; it migrates, collects lint, and eventually reaches the thread and fabric.
This is a well-understood engineering problem rather than a folk warning. A patent covering hook lubrication systems describes the design challenge as ensuring adequate lubrication of a high speed hook without providing an excessive amount of lubricant, which will soil the work and be wasteful, and includes a porous felt element specifically to prevent slugs of oil reaching the fabric after the machine has stood idle. If industrial designers engineer against oil marking the work, a home user with an oil can should be at least as cautious.
Run a scrap afterwards
After oiling, always sew a test piece before returning to your project. Use light coloured scrap, since oil marks show most clearly there, and sew a decent length so any residual oil in the hook area transfers to the scrap rather than a garment. Some people leave the machine standing for a few minutes first with an absorbent cloth under the needle area.
If oil does reach a project, do not iron it. Heat sets oil marks. Treat the mark before laundering, following the fabric’s care instructions.
Frequency and storage
For machines that take oil, a common manufacturer interval is every eight to ten hours of actual sewing time, or before a large project after a long idle period. Frequency of use matters more than calendar time.
Between projects, keep the machine covered. A hard case or a fabric cover keeps dust out of oiled surfaces, where it would otherwise stick. Store in a stable, dry environment rather than an unheated garage or loft, since condensation on cold metal encourages surface corrosion on precisely the parts you have been protecting.