Most people assume sweat is what causes body odour.
It doesn't.
In fact, fresh sweat is virtually odourless. The smell most people associate with sweating only develops after sweat reaches the surface of your skin.
Here's what's actually happening.
1. Sweat is mostly odourless — until it meets skin bacteria
Human sweat is produced by two main gland types, each with different biochemical profiles:
Eccrine glands
- Found across most of the body
- Produce a watery secretion composed mainly of water, sodium chloride, and small amounts of lactate and urea
- Primary function: thermoregulation (cooling the body through evaporation)
- Fresh eccrine sweat is essentially odourless
Apocrine glands
- Concentrated in areas such as the underarms and groin
- Become active during puberty
-
Produce a thicker secretion containing:
- lipids (fats)
- proteins
- steroid-like compounds
On its own, apocrine sweat is not strongly odorous. The smell emerges after interaction with skin microbes.
2. The real cause of body odour: bacterial metabolism
Your skin hosts a diverse microbiome, including bacteria such as Corynebacterium and Staphylococcus hominis, which play a major role in body odour formation.
These bacteria metabolise components of apocrine sweat through enzymatic breakdown, particularly:
- amino acids
- long-chain fatty acids
- sulfur-containing compounds
This microbial activity produces volatile organic compounds (VOCs), including:
- thioalcohols (strongly associated with underarm odour)
- short-chain fatty acids
- ammonia derivatives
These VOCs are what we perceive as body odour.
So the equation is:
apocrine sweat + skin bacteria metabolism → volatile odor compounds
Importantly:
- Sweat volume alone does not determine odour intensity
- Microbial activity and sweat composition are the key variables
3. Why antiperspirants reduce odour (and how they work)
Antiperspirants are not primarily antimicrobial products. Their main mechanism is physical.
Most contain aluminium-based salts (such as aluminium chlorohydrate), which:
- dissolve in sweat
- form a gel-like plug within sweat ducts
- temporarily reduce sweat secretion at the skin surface
With less moisture reaching the skin:
- bacterial growth conditions become less favourable
- substrate (sweat components) available for bacterial metabolism is reduced
- odour production is indirectly decreased
However, because this approach reduces sweating itself, it can also:
- alter local skin hydration and barrier function
- affect thermoregulation in treated areas
- change the microenvironment of the skin microbiome over time
4. A different approach: managing odour at the microbial level
Unlike antiperspirants, deodorants do not block sweat ducts.
Instead, their primary function is to reduce odour formation on the skin surface.
Science-backed deodorant strategies typically work by:
- reducing populations of odour-producing bacteria
- inhibiting bacterial enzymatic activity
- shifting skin surface pH to less favourable conditions for VOC formation
- using fragrance compounds to mask residual odour (in some formulations)
POSTCARD deodorants are designed around this principle: supporting odour control without suppressing sweat production.
This means:
- sweating still occurs naturally
- odour formation is reduced at the microbial level
- the skin environment is maintained rather than blocked
5. Why body odour varies from day to day
Body odour is highly dynamic because it depends on multiple biological and environmental variables:
Physiological factors
- Hormonal fluctuations (including androgens, which influence apocrine activity)
- Stress-induced sweat changes (adrenergic signalling alters sweat composition)
Lifestyle factors
- Diet (e.g., sulfur-containing foods can influence VOC precursors)
- Hydration status
- Sleep and metabolic state
Skin environment factors
- Existing microbiome composition
- Skin pH
- Temperature and humidity
- Friction and occlusion from clothing
Hygiene and timing
- Residual bacteria levels on skin prior to application
- Timing of product use relative to sweat onset
This variability is expected — body odour is a dynamic biochemical process, not a fixed trait.
6. The takeaway
From a biological standpoint:
- Sweat is primarily a thermoregulatory fluid
- Body odour is produced by microbial metabolism of sweat components
- Odour control can be achieved either by reducing sweat availability or by modulating skin microbial activity
Antiperspirants address the first pathway.
Postcard's Deodorants focus on the second.
Understanding this distinction reframes freshness not as “stopping sweat,” but as managing the biochemical interactions that occur after sweat reaches the skin.
