Noise-Induced Hearing Loss vs. Age-Related Loss: Reading the Audiogram

What does noise-induced hearing loss look like on an audiogram?

Noise-induced hearing loss typically shows up as a notch centered around 4000 Hz, with hearing recovering somewhat at 6000 and 8000 Hz rather than continuing to decline. That notch shape reflects how the ear responds to noise exposure: the 3000 to 6000 Hz range is where the cochlea is most vulnerable to mechanical damage from sustained sound pressure, while the acoustic reflex offers some protection at lower frequencies and higher frequencies are affected less by the same exposure pattern. Early on, the notch is a clean dip that returns toward baseline by 8000 Hz. With years of continued exposure, the notch deepens and widens, sometimes flattening into a broader high-frequency loss that starts to resemble other patterns, including age-related decline.

What does presbycusis look like by comparison?

Age-related hearing loss, or presbycusis, produces a downward-sloping loss across the high frequencies without the notch and without recovery at 8000 Hz. Instead of dipping and rebounding, the line on an audiogram keeps declining as frequency increases, and both ears typically show a similar, symmetric pattern. Presbycusis develops gradually over decades regardless of occupational noise exposure, so an employee with no history of loud work environments can still show meaningful high-frequency loss by their fifties or sixties. The absence of a distinct notch, combined with bilateral symmetry and a pattern consistent with the person's age, is what points a reviewing professional toward presbycusis rather than noise exposure.

Why does the distinction get harder over time?

The two conditions are additive, and in older workers with long noise exposure histories, aging can blunt or fill in the notch that would otherwise flag noise as the primary cause. A worker in their twenties with a clean 4000 Hz notch and normal thresholds elsewhere is a straightforward noise-induced case. The same worker at 55, after three more decades of both noise exposure and normal aging, may show a broader high-frequency loss where the notch is no longer distinct from a sloping presbycusis pattern. Without access to that worker's baseline and intervening annual audiograms, a single audiogram taken in isolation may not reliably separate the two contributing causes.

Feature	Noise-induced hearing loss	Presbycusis
Typical shape	Notch near 4000 Hz	Downward slope, no notch
8000 Hz behavior	Often recovers somewhat	Continues declining
Symmetry	Can be asymmetric with unequal exposure	Usually bilateral, symmetric
Onset	Tied to noise exposure history	Gradual, tied to age
With long exposure	Notch can deepen and widen	Not exposure-dependent

Why does this matter for a hearing conservation program?

Distinguishing the two patterns matters most when a reviewing professional is deciding whether a confirmed standard threshold shift under 29 CFR 1910.95 reflects a workplace exposure problem or an aging trend that program adjustments will not change. If a series of annual audiograms shows a symmetric, notch-free, slowly progressive high-frequency pattern consistent with the employee's age, that supports a presbycusis explanation and may not indicate a need for additional hearing protection measures. If the pattern shows an asymmetric notch, especially in a younger worker or one whose loss is concentrated in the ear closest to a specific noise source, that points toward an exposure issue worth investigating, whether through re-evaluating hearing protector fit, area noise monitoring, or engineering controls. OSHA's Appendix F age-correction tables exist specifically because both conditions can contribute to the same audiogram, and the agency provides a statistical way to separate the age-related component from the STS calculation. See Foster's guide to Appendix F age correction for how that adjustment works in practice.

How does Foster document this distinction?

Foster's audiometric technicians record year-over-year threshold data at every test frequency, not just the three used in the STS formula, so a reviewing professional has the full audiogram history needed to see whether a notch is present, whether it is deepening, and whether the pattern is symmetric between ears. That history goes to the employer's designated reviewing professional along with each year's results, rather than leaving the interpretation to a single audiogram read in isolation. For employers running hearing testing programs across a workforce with a wide age range, that consistent record-keeping is what makes it possible to tell a presbycusis trend apart from a noise problem that needs attention, instead of guessing from one test.

Frequently Asked Questions

Can someone have both noise-induced hearing loss and presbycusis at the same time?

Yes. The two conditions are additive rather than mutually exclusive, and many older workers with long noise exposure histories have some combination of both contributing to their overall hearing loss.

Does a missing notch mean noise exposure isn't a factor?

Not necessarily. Continued noise exposure over many years can deepen and widen an early notch until it blends into a broader high-frequency loss pattern that no longer looks like a classic notch, even though noise contributed to it.

Who decides whether a shift is age-related or noise-related?

The reviewing professional named in the employer's hearing conservation program makes that determination, using the full audiogram history rather than a single test result.

Does OSHA require testing at 8000 Hz?

29 CFR 1910.95 requires audiometric testing at 500 through 6000 Hz at minimum, though many programs, including Foster's, test through 8000 Hz because that frequency helps distinguish a recovering notch from a continuing slope.

Does age correction remove the need to investigate a shift?

No. Age correction under Appendix F only adjusts the STS calculation. A reviewing professional can still recommend follow-up based on the raw audiogram pattern even after age correction is applied.

Foster tracks full-frequency audiogram history across every annual test. See on-site testing for program details, or request a quote to set up a hearing conservation program.

Sources

• 29 CFR 1910.95 Appendix F, OSHA
• ACOEM Guidance Statement, Occupational Noise-Induced Hearing Loss