The risks: damage, disqualification, health
Everything described so far — the swelling mechanism of 14.3, the regulatory grey area of 14.4, the products of 14.6 — could be read as a practice without cost. It has one, and it is worth knowing before deciding.
Damage to the rubber. The cycle of swelling and contraction a boost imposes on the sponge is not free. Every application stretches the cell walls beyond their natural state; every evaporation returns them to a position that is no longer exactly the original one. Over time the structure loses resilience. The thinned walls do not recover their full thickness, the cells remain slightly deformed and the sponge responds with less life even when freshly treated. It is accelerated ageing: the rubber does not fail, but its useful window shortens. A sponge that untreated would hold its properties for months may need replacing much sooner if subjected to frequent cycles of boost. Section 4.6 described the natural degradation of a rubber; treatment accelerates it.
The topsheet suffers from the process too. On rubbers with a tacky surface, oil migrating from the sponge towards the upper sheet can reduce the grip of the rubber — precisely the quality that defines those rubbers. On tensor rubbers, where the surface depends on elasticity rather than tackiness, the effect is smaller but not nil: a topsheet subjected to cyclic stresses loses uniformity of response sooner than an untreated one.
Disqualification. Section 14.4 explained that the VOC tester does not detect modern oils applied far enough in advance. But the risk does not end with the chemical detector. A treated sponge swells, and that swelling can take the total thickness of the covering beyond the 4.0 mm the rules allow — the limit described in 3.2. Umpires measure the thickness with a gauge before matches in official competition. A freshly boosted rubber, at the peak of its expansion, can exceed the limit even where the factory sponge was within the margin. A player who misjudges the time between application and competition is exposed to a disqualification that has nothing to do with the chemistry of the product and everything to do with a visible, measurable physical figure.
Outside international events the risk of sanction falls considerably — as noted in 14.4 — but it does not disappear. Any national federation can apply the checks where it has the instruments, and the closing rounds of national championships usually include equipment inspection.
Health. Today's boosters are less aggressive than the speed glue banned in 2008 — that did contain volatile solvents toxic by inhalation — but they are not inert. Refined mineral oils irritate the skin on prolonged contact. Synthetic formulations include compounds whose safety data sheet recommends ventilation and gloves, though few players read that sheet. The risk is not comparable to breathing solvents in a closed hall during a tournament, but repeated exposure over months or years has not been studied rigorously in a sporting context. Elementary prudence — applying in a ventilated space, avoiding direct contact with the skin, washing the hands afterwards — reduces the risk to reasonable levels, but it is worth knowing that it exists.
None of these three risks invalidates the practice on its own. What they do is put a price on it: a shorter working life for the equipment, a regulatory exposure that depends on the competitive context, and a minor but real health precaution. Whether to accept that price is the player's decision, and the position this book takes on it is set out in 14.8.